I have a Pioneer 50", and got Gordon (of ConvergentAV fame) to calibrate it - and yes, it is worth it. You'll notice much more detail, as most, if not all, plasmas are set up at the factory with the wick turned up way too high.
Having seen Gordon's work again at the HiFi show in Glasgow, I can tell you it is well worth the effort. There was two displays running a comparison, one out of the box and the other after calibration.
Out of the box, you could clearly see that it required some adjustment. I'm sure that you or I could improve on the initial state.
Calibrated screen just looked perfect. Colours, blacks etc were just correct - as it should be. There was a big difference between the calibrated and uncalibrated display.
Looking around the whole show was very interesting. Linn had quite a system running, but surprisingly it wasn't the best on show. That was Acoustic Reproduction Technology (www.loudspeaker-art.com). Their reference system was the best I've ever heard, and I was totally amazed at it's performance.
John thanks for nice comments about the calibrated plasma at the show. The idea of that stand wasn't just to show calibration but to show that having the knowledge of how to configure things properly is a big benefit too.
I am currently taking bookings from those interested in getting the most accurate performance from their displays.
You may also be interested to know that HCC commissioned an article about calibration which should appear in their new Annual Hi-end magazine out in a few weeks.