I've just got myself another Powerbook, a 1.25Ghz 15" with 1Gb RAM and did my usual prep routine of fresh Leopard install, all updates, then all eye candy and CPU hogging tricks turned off with the Secrets pref pane. However, performance has been a little sluggish - I know I've still got room for another 1Gb of memory but I don't want to spend any more at the moment. It's surprised me, as I had a 1.33GHz 12" Powerbook with 768Mb RAM running Leopard fine but I think the combination of slightly less CPU and more pixels to drive on the screen has this one just under the threshold of decent Leopard performance. I haven't used Tiger for years (apart from on my G3 iMac) - I naturally opted for the more current OS given the hardware specs always covered it, so I did an inventory of all the apps I use and was astonished to find 95% either run on Tiger as well or offer earlier versions for it! So with nothing to lose, I installed Tiger...and what a difference! The OS runs like lightning - and even better, a lot of apps seem to use less resources under Tiger. VLC for example, is using 20% CPU, whereas on Leopard, with the same movie, would run at 35-40%. I think if the apps you use are available under Tiger and you have a machine hovering at the Leopard threshold, switching back to Tiger might breathe new life into your Mac.