No, I have been having the exact same issues, both under 2.6.5 and 2.7.3 (Pro). I'm running OS X 10.1.5 on a dual G4/450 with 768MB of RAM. This system bogs down the same way, taking five seconds to show what I'm switching to, refresh the screen, etc.

It may be something to do with the Java 2 implementation on OS X, but as the original poster didn't say which exact Win OS he's using, hard to tell. All I know is, I've been using 2.7.3 Pro for three days now, and last night, the slow down started, and has not gotten any better after a full system reboot and a cache clearing...