There's been some discussion on Mac forums about an Exposé slowdown in 10.4. The slowdown is allegedly due to the new feature introduced in Tiger called Automated Beam Synchronization. Using Quartz Debug from Developer Tools it is possible to temporarily disable Beam Sync.
If you're interested in more permanently disabling Beam Sync, read on...
This thread at CocoaBuilder.com demonstrates code for programmatic disabling of Beam Sync:
extern void CGSSetDebugOptions(int);
extern void CGSDeferredUpdates(int);
typedef enum {
disableBeamSync = 0,
automaticBeamSync = 1,
forcedBeamSyncMode = 2
} beamSyncMode;
beamSyncOption mode = disableBeamSync;
CGSSetDebugOptions(mode ? 0 : 0x08000000);
CGSDeferredUpdates(mode);
It needs to be linked against QuartzCore. If you rather not deal with coding, you can use a simple command line tool called beamsync. Running beamsync with the -d option disables; -a makes automatic, and -f forces beam synchronization. The source code is available as well. Note that both the tool and the code rely on the undocumented API, which is a subject to change in the future Tiger upgrades. It's provided as is; use at your own risk.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050622224239730