I can't find the link, but someone asked the same question on AVS forum the other day. The response is that it's a non-issue with Plasma....less than 1ms.
They are PWM, so you can't directly identify the response time, sort of like DLP. What I was getting at is that there is a phosphor decay time, so there are temporal hangs that occur.
The reason I asked why you asked is because what prompted this question? What kind of content are you going to be viewing, what will you be doing with the plasma? There's the immediate response time, and there's also the decay time, and they are different with different kinds of displays. Depending on the use of the display, these things may ore may not be significant obstacles.
So, it would be best if you just explained why you're asking this question, so we can give a meaningful response.
For example, you can think of a CRT as having pretty much instantaneous rise time, but there is a significant decay depending on the phosphor type. If you were doing 3d stuff, this is a big problem. If you were doing stuff like gaming, this isn't a problem.
I'm a little fuzzy on this "rise" vs. "decay" time. Is "decay" time only an issue when dealing with a fast moving object on a dark or black backround? Would "decay" time be eliminated with a color change of say green to red because the "rise" time of red is nearly instantaneous?
I wouldn't be concerned about the plasma for that use. I mean, I suppose if you were a picky gamer or something. Go look at plasmas and see what you think for yourself.