also, aside from the things that ernesto mentioned, which are all correct, you have better response to compression artefacts and picture details in LCD. To see the same thing on a Plasma as an LCD you have to sit further away (reducing the relatvie perception of screen size).
Plasma contrast ratios tend to be higher, but LCDs have recently improved a lot, and continue to do so. However, the ghosting problems on Plasma tend to negate this under most circumstances.
Plasma tends, also, to get much hotter when running.
In short, LCD = better. New LCD = higher contrast than old.
Caveat - make sure to check it before you buy it, many crappy LCDs have colour pitch problems that push them towards purple.
I keep telling everyone to wait for SED, but they have not yet announced a shipping date for them. Might know in September though.