Aren't plasmas quite a bit heavier than LCDs? Also I think people have an impression that plasmas have image retention issues, true or untrue. Also all the large plasmas I've seen in big box stores had noisy fans, and I want as little ambient noise as possible from my screen, as I use it primarily for web browsing
Heavier, generally. I wouldn't want to move my 50" plasma around by myself. My 42" LED, on the other hand, is super light in comparison.
Image retention issues are largely minimized in modern plasma displays, it seems, but it's still a factor to consider over LCD depending on how you use the display (i.e. general usage not worth worrying about, but constant, static images might be different). The worst I've noticed is static UI elements in games that are retained for a very brief moment when transitioning to a black screen after a couple hours with those elements on the screen originally. Not an issue at all.
Plasmas I've had experience with tend to "buzz" but don't have much in the way of fan noises. A lot of people exchange out units until they get near silent ones (i.e. not able to hear in a normal sitting/viewing location). My Panasonic buzzes and can be heard from a few feet away, but it gets completely covered by ANY noise and seems to be getting quieter as time passes. I also mounted some cheap/simple material behind the display to diffuse and absorb sound waves.
My main complaint is that plasma displays look noisy/grainy up close compared to LCD, but it's not a factor from a normal viewing position. Power consumption is pretty poor...I've seen the TV draw ~150-200 watts.
But, calibrate the display, pop in a good Blu-Ray movie, and turn down the lights, and the overall picture quality is too good to worry about such minor negatives/differences relative to LCD.