Bright people surround my life, but I am often surprised when conversation steers to HDTV. Many of these otherwise intelligent and technical savvy people make basic mistakes. HDTV is not a ‘core-comptency’ of mine, but I am confident that this is a list of some basics many people get wrong all the time:
Video Cables:
DVI/ HDMI are the best – these carry purely digital signals. HDMI is an upgrade on DVI, you can buy converters between them both, but DVI cannot carry audio signals or handle HDCP.
Component video is the second best choice. It is (generally) analog and can carry any resolution up to 1080p; I have no experience, but would worry about picture quality at 1080 with a long cheap cable.
S-Video, composite. Look at a calendar, it is 2007 in a few days time!!!
VGA – not a bad choice if you must, but it is the equivalent of coding in Pascal because that’s the only compiler you have handy.
Monster HDMI/ DVI cables:
No, no, no! You just do not need high-end cables for digital signals traveling short distances. In the analogue days we were always struggling for ‘the clearest sound or color’ – with digital if the signal is not working you know immediately. Have you ever heard of $100 premium monster IDE cables for a hard disk? Did not think so, but I could start a new business PremiumCablesForSuckers.com 
I happily ran a 480p Plasma on a fifteen foot DVI cable from froogle that cost under twenty bucks. Mileage may vary with the higher frequency of 1080p, but I’d try the cheap cable before splashing the cash on a premium brand.
Sound Cables:
Yes monster cables ‘may’ help when joining an amp to speakers, but 99% of the audio quality is a function of the wire’s gauge. 12 gauge mains cable from the Home Depot will kick the pants off 16 gauge Monster cable – trying to route 12 gauge solid core through your walls is not that easy though, ask me how I know I settled for an off brand 14 gauge multi-core for surround speakers and short runs of expensive cable for only the front speakers.
Of course all your digital cables should be optical. These no longer need to be special ordered from NASA, and can be found on Froogle for under a dollar if you look hard enough. I have a box full of different lengths + optical splitters/joiners – they cost peanuts and work fine. Coax digital cables also work fine, but would you rather be Buck Rodgers or MacGyver? Buy the optical
Resolution:
HDCP is beginning to matter. People with real lives (mortgages, kids and everything!) are starting to buy 1080p projectors/ LCDs…. before you do make sure you read up on HDCP (High Definition Content Protection). All new HD players will have HDCP, and consequently to play content at 1080p, your HD Monitor must also support HDCP. If your monitor does not support HDCP then the player will revert to a lower resolution 
Note: Wikipedia says HDCP will work over DVI, but I would play it safe and use a HDMI cable.
In all likelihood HD DVD movies CSS-equivalent will soon be cracked [are you there DVDJon?]. Many people in the know will play 1080p content by means other than HDCP enabled boxes, a hacked xbox 360 or PS3 perhaps? HDCP like DRM will only harm the masses who are not even aware of the acronyms. Pirates and the tech-savvy will simply steer around them.
Screen Type:
Linux or Windows, Optimus Prime or Magneto? Yes this is religious territory, but here goes:
Plasma: Now start at $700 for 42″, great picture in brightly lit rooms, some screen fade/burn over time, bad dark levels, will soon be pushed aside by LCD + eventually SED
Projectors: Really big screens for not much money. Front or rear projection. Your own screen and projector in a basement is the ultimate in Home Theater but it had better be pretty dark in the room. Probably not suitable for a main TV, though many people choose the rear project units and seem to love them
LCD: 40″ 1080p is currently $1500. Prices continually falling – in raw materials terms these must be cheap to produce and will surely cost next to nothing soon. Their refresh rates and viewing angles have massively improved recently
SED (Surface-conduction Electron-emitter Display) looks promising but don’t expect to be affordable until 2008 at the earliest
CRT: Forget it, large flat screens are now so cheap it is not worth considering a CRT, although CRT has the best picture quality of any technology. They simply become to large and heavy to make a screen to rival the benchmark 42″ Plasma.
Sound:
The AV community seems to be agreeing that 5.1 sound is perfect for home theater system. 6.1 and 7.1 (SDDS?) have not made much impact. Make sure your receiver/ amplifier can handle DTS. DTS is ‘premium’ 5.1 sound and I believe is compressed less than most 5.1 sounds tracks. I like to think it sounds better, but my ears have witness too many loud clubs and rock concerts for me to be sure. If you live in a detached house and like action movies then buy a big sub – you’ll thank me later.
1080i, NTSC, PAL:
People almost never get this without 20+ minutes of explanation. Summary: all modern display technologies are progressive. If a LCD or Plasma says it is 1080i then it means that it will scale a 1080i image to its native resolution. Check the native resolution when buying a screen, telling a home theater buff that you just bought a 1080i LCD screen is like telling a web developer that Java coding will be easy because you did some JavaScript on your myspace page. He’ll probably pat you on the head before returning to his online dispute on whether Gredo or Han Solo fired first.
PAL, NTSC, SECAM etc also confuse most people. These days the conversion is done very well for you so don’t worry about this too much.
Resolution
Everyone understands the basics, if you want to recap then I suggest starting with the illustration at the bottom of this Wikipedia page on 1080p.
To summarise resolution: I have a 480p plasma which looks great playing DVDs compared to an old plain-Jane CRT 32″ TV. Most people consider 720p to be the start of real High Definition. Personally I bought the cheaper 480p as a stop gap to buying an 50″ 1080p screen when they become affordable. At this moment in time a 1080p screen with HDCP and at least two HDMI inputs looks pretty future proof – if you plan on keeping a screen for the next ten+ years, seriously think about spending the extra cash or waiting for prices to drop a little more.
As stated earlier I do not consider myself an expert in this area, but through Podcast Osmosis seem to have picked up some basics. Wikipedia had great coverage on HDTV acronyms, expect to lose a few evenings of your life there before buying that new HDTV. Buyers regret will happen anyway, whatever you buy will appear overpriced outdated junk by the time January 2009 rolls around.