(Getting back on topic.)
I noticed the same behaviour in OS X Lion GM as the OP. The OS seems to be using 5-10% of the CPU continuously (shown as 20% out of 200% in Activity Monitor):
Image
(No applications running but Activity Monitor. "mdworker" happened to be active at the time but it's usually idle.)
It's always the same processes that use CPU time:
SystemUIServer,
WindowServer / to a lesser extent:
mds,
kernel_task / periodically:
mdworker:
Image
Generally, this GM feels sluggish. The most obvious aspect is scrolling: not spot-on in sync with the scroll gesture like in v10.6.8. Whether on web pages (Safari) or generic scrollable window items (as in Finder, vertically or horizontally).
As a consequence of the constant CPU usage, battery life is destroyed. My guess is it's almost halved. The most I get is 4 hours*, browsing websites (Safari, Flash deactivated) and watching 720p H.264 videos using VLC.
[url=http://img269.imageshack.us/img269/8986/screenshot20110709at802.th.png]Image[/URL]
Note that the computer in question is no workhorse: MBA equipped with an old-ass C2D, 320M, 4 GB of RAM. Still, SL is snappy, feels light and responsive. Bearing this in mind, and seeing those background system processes taking this much CPU time, I'm hopeful Apple will optimize the heck out of Lion in the next iterations.
After all,
"premature optimisation is the root of all evil" (most of the time). I'm sure the developers have kept CPU and GPU efficiency in the back of their mind all along though. Now that all features are in place and working well (in my experience), these upcoming final iterations are their opportunity to optimise.
* About battery life and CPU usage of background system processes: I have yet to compare those extensively with SL. Prior to Lion, SL was installed for a day only, didn't have a chance to test battery life or watch CPU usage but from what I remember, those processes were behaving (idle or close) and estimated remaining time on battery was a lot more optimistic than what I'm getting now.