i researched this for months while i was saving up for a new tv this spring and i was surprised to find out that plasmas are not only still a relevant technology, but a superior one when compared to lcds. the big issue with plasmas is phosphor lag. when i first got my 42 inch panasonic g10 in june, i could definitely see some minor phosphor trails. it wasn't a huge problem, but you could definitely notice it. however, after some time (i'm not really sure how long), i couldn't see them anymore, even if i specifically try to spot them. people said that they usually become less of an issue over time, but i didn't realize that they would seemingly go away altogether.
overall, i love my g10. i didn't even need to waste time calibrating it because i have been very satisfied with it's THX mode. it only cost me $1000 in june.
with lcds, you need to consider issues like motion blur and input lag, both of which are permanent and detrimental to gaming.