I'm using the xfce4 DE and sometimes (usually) when I resume from suspend some features are lagging. The whole firefox window is grey, keyboard shortcuts defined in settings->keyboard->application_shortcuts don't work (the ones in settings->window_manager->keyboard do work), and touchegg doesn't recognize multitouch gestures. The lag takes about 10-30 seconds and then everything's fine. However I am able to navigate through workspaces and use zsh. There has also been few times this has happened just out of the blue without resume from suspend.
I'm aware this sounds a very vague description of the problem but I've been unable to find out anything more. My distro is Arch if that makes difference.

I have a wireless KVM switch that causes the same issue when I flip it between systems. I can get information on it (though I can't seem to fix it) by setting up a terminal and typing in

sudo tail -f /var/log/messages

Then flipping the system over (for you, letting yours go into suspend) and then back (you wake yours up). You should see the hardware logging getting written into messages (at least that's the way it works on Slackware). Give it a try and post back what it's saying if anything.

This webpage seems to be maintained by a XFCE developer (and I base that on his manic interest in complete bug reports) who gives you more detailed instructions for debugging the WM

And of course, you can just do what I do which is bang the mouse against a handy surface until it wakes up. I'm not sure it's a productive strategy, however the 'sleep' period doesn't seem to last as long if I'm whacking it on the desktop, of course that could be a subjective assessment.