I finally installed Lion yesterday on my 2008 Penryn MBP. I did the regular upgrade install.
Today it seems to be running significantly cooler to the touch than with Snow Leopard. This is not from reported temperatures (I haven't checked), but the left palm rest area used to get really warm if plugged to AC for awhile (I am at work most days.)
It's been powered on and plugged in all day today, and while it feels a little warm its much cooler now, and not uncomfortable at all.
So far I like Lion, but its different enough that I can see how it would throw off some people's workflows. The only thing I wish for is some default gesture to switch tabs in Safari and other apps. I tried BetterTouchTool, but I am getting a weird bug where it switches the 3-finger Mission Control Swipe to 4-finger (even though it still says 3-finger in System Preferences.)