I just installed Intrepid on my dual head machine at work and the experience was without flaw, easier than ever.
I have an ATI card, running lspci gives me RV515 PRO (Radeon X1300/X1500 series) and the default drivers work just fine, going System -> Preferences -> Screen Resolution and unchecking Mirror Screens took care of everything, starts to be as easy as in Windows, yay!
However, after doing an upgrade I notice that I’ve got new proprietary ATI drivers available, ATI/AMD proprietary FGLRX graphics driver to be exact. So I enabled them and my dual head setup was gone and I couldn’t get it back without Googling and messing around for hours and I’ve made a promise to myself to never ever do that again so there we are at the moment, the rest seems to be working just fine.
The only difference I saw straight away (apart for the easy dual head setup) is more effects out of the box expanding upon what was already in Hardy. Windows and menus now fade in and out for example. That all disappeared though after I screwed up with the proprietary drivers so now I’m back with no effects at all. It happened after running in repair mode and choosing an alternative to fix the x-server (also new for Intrepid), it did so but it removed all kinds of eye candy at the same time.
Update: I just got help with the missing effects from Sugree Phatanapherom, the Thai geek overlord. This is the walk through if you’re sitting in the same situation that I describe above:
1.) Search for fglrx in synaptic, completely remove everything you get there except the jockey manager and the original xserver-xorg-video-radeon driver.
2.) Reboot and see the effects in action again!
Update: I just installed on my Acer laptop, for the first time everything just worked without hassle, some desktop effects, sound, dimmer and the wireless, good job! Check it out, running Black Reuben.