First off, I am just going to say "LCD". LED is a type of backlight for an LCD so I am not going to qualify it.
Nobody is making a "high end" LCD w/ CCFL backlight anymore. They are all LED.
LCD vs. Plasma: I've noticed that the height/width of the TV as a whole for a 50" plasma will get you a 55" in the LCD. This is because of the bezel.
Very true on most of them, the higher end Panasonics (GT/VT) are surprisingly thin. I think the new LG leds have the nicest bezel and stand, but thats my personal preference rather than a functional issue,
LCD vs. Plasma: There is a big difference in the weight of the two with plasma being much heavier. This seems to be because of the glass (plasma).
Correct. The other reason plasma gets more glare is because it is two pieces of glass sandwiched together, doubling reflection. Again, higher end ones are using different kinds of materials now.
LCD vs. Plasma: In the past, LCD would have a matte finish front and therefore be better for bright rooms. From what I've read, the newer LCDs are now using a glossy front, perhaps to make colors better, so YMMV if you have a bright room.
All Samsung LEDs are glossy, Sony uses both, Sharp is mostly matte, LG uses glossy on their nice ones.
You can also get full LED backlit LCDs now which might give a better chance of not having "clouds" around the edge of the LCD which seems to be a problem with edge-lit LEDs (clouds are the backlight leaking around the LCD panel). I am probably going to recommend a 55 or 60" LCD with full LED backlight for my Dad.
Very few tv's have full arrays (as opposed to edge lighting) and they are the most expensive. Sony HX929, Vizio XVT, Sharp Elite are to my recollection the only ones sold last year. You will see other phrases tossed around like microdimming and local dimming. Each company uses different marketing talk. Edge lighting allows them to be thinner.
It is hard to see the problems with edge lit tvs in the store with their odd lighting. It is much easier to see the "flashlighting/fogging" when you get home. All cheaper LEDs suffer this, no matter the brand.