Edge lit and direct lit 55-60" sets look like they use about 70-80W. What's interesting is the 60" Panasonic UT50 plasma only uses 139W. So it's not a huge difference between the two.
Again, visit CNet & look at some of their reviews: they usually (always? Or perhaps for all plasma sets & Larger LCD models) include Power Usage results for OOTB AND Post-Calibration.
That should give you some idea of real-world power usage.
Consumer Reports also gives an "Energy Cost Per Year" figure (in $; based on 5 hours usage daily), which provides relative power consumption.
Most plasma panels are more efficient than in the past, & Power COST is scarcely a factor anymore: Per CR, our 60ST50 costs about $4.50/month to operate. Certainly, that is more than LCD panels cost, but still not a high enough figure to warrant placing into OUR purchase decision matrix.
Lower energy consumption should yield lower heat output. But while we do not notice any General Room Heating effect from our 60" panel, would be lying to say that, IF you get close enough, there was NO heat radiating off the screen. But I need to get within inches to feel it.
Again, take some time to read a number of reviews - and also to visit owner's threads to see what they think about their panels.
Always remembering that A) People with problems - or axes to grind - often find their way to Owner Boards; and B) These are sometimes offset by Pollyannas who claim NO FLAWS WHATSOEVER for their chosen panel....