1. As a general rule LCDs are as good as Plasmas up to 42", above that Plasmas are, as yet, better.
2. Plasmas are better in dark conditions are have a faster response time - i.e. better for sports. LCDs are much better than they were, but fast action can still show some lagging/smearing.
3. LCDs use less power and in theory have a longer life, but even plasmas will last for around 30K hours before losing half their brilliance. Work out the number of years that is at your weekly viewing hours; it wasn't a relevant limitation for me.
4. Blu-ray movies are recorded in 1080p, HD TV in 1080i, hence a 1080p TV is best to cover all needs, but is only a factor for 42"+ screens, below that the pixel count means anything in 1080p will be downscaled anyway.
5. 100hz sets double the refresh rate giving the same update rate for 1080i as you'd get using 1080p.
6. it's getting like hi-fi, there are lots of esoteric features and companies claiming more contrast, magazines telling you how to adjust the settings etc -but 99% of people wouldn't be able to tell the difference.
Recommendation? Go look at an LCD "HD Ready" (1080i) screen playing a fast action Blu-ray movie and some sports against a 1080p plasma; if you can't see the difference buy the cheaper.