I absolutely LOVE my Panasonic 42" plasma.
I set it to something very conservative, definitely nowhere close to "vivid", but a bit brighter than "cinema". It works well for hockey, dramas, etc... in my living room. I flip it to the preset Cinema mode for movies and it works well this way with less ambient light in the room.
Break-in isn't wholly necessary but I took extra precaution upon suggestion from gurus on avsforum(s?).com and ran stretch-screen on SD 4:3 stuff, for about a month. The Panasonic "JUST" mode actually stretches the edges progressively more than the middle, and this is less "squished" to the eye than a fully stretched 4:3 pic. Anyhow, the result of this was no chance of black 4:3 bars causing uneven colours (especially whites, like hockey rinks!) where the black bar would begin. I know the chances of this happening are slim-to-none on recent sets, but my friends' cheaper Hitachi from 3 years ago has problems with this (but he's returning it to The Brick a few months before his extended warranty is up, for guaranteed replacement with the newest TV in that pricepoint... LOL!).
Enjoy your new TV.