Here is my experience to date (upgraded to Lion on day 2):
Early 2009 24" iMac:
-Video performance is just fine.
- Applications such as Photoshop CS4 (after Java update) works great.
-Windows7 virtual machine using Parallels (after update) works better
than on Snow Leopard.
-Safari faster/snappier
-Basically, Lion has been a pretty ho-hum update.
2011 13" MBP i7:
-Pretty much all the comments for my iMac hold true with this guy
-Some have said battery life is killed, I actually see my battery life
improved and machine actually running 5 degrees cooler.
2010 Mac Mini:
-DISASTER!!!!!!!!!!!!!!!!!!!!
-Severe problems with auto discovery/HDMI handshaking not present
with Snow Leopard.
-Any deviation whatsover from ONE!!!! start up sequence results
in NON-FUNCTIONAL VIDEO!!!!!! Only fix is to shut everything
down start up everything in THAT ONE SEQUENCE plus zapping
PRAM, then going into display preferences changing them and then
changing them back, is the only way to get a good start up next
time. Oh yeah and start up with THAT ONE SEQUENCE.
-Turn off display while Mini on and turn display back on later.
BORKED VIDEO as stated above. Jump through hoops again.
-Also, when the prevous situation occurs, "option" or "command+R"
does not work, well it might be but can't tell since VIDEO IS BORKED".
-The plus side is, that when things boot normal, performance is really
good
-PLEX works fine and is still probably the best app for playing back
h.264 video.
-XBMC works great as a DVD playback. The best at MPEG-2
video playback.
-Netflix via Safari works really well.
None of my systems have any issue with sluggishness or degraded
performance (in the case of the Mini when it boots).
If you say there is major sluggishness, then check process monitor
for how much RAM is used and identify which process is hogging up all
the CPU.