Did you do an upgrade, or fresh installation? I'm running a late 2007 macbook (the santa rosa revision), and it definitely runs a little bit hotter under lion. For most tasks speed & responsiveness are basically unchanged in my experience - except for scrolling, particularly in safari.
In addition to the RAM hogging, I also find scrolling in safari is not nearly as smooth compared to older safari versions on SL. I wonder whether this is due to the method apple uses to hardware-accelerate scrolling, as turning off acceleration for the whole OS X UI in Quartz Debug gives much smoother scrolling. I don't think it's an issue of graphics horsepower either - at least on 10.7.0, all the macs at my local apple store suffered from less than silky smooth scrolling, even a mac pro with a fairly powerful graphics card. Will have to go back and check at some point to see if 10.7.1/2 improves things...