I just recently purchased a XPS 15z and so far I'm fairly satisfied.
The nvidia optimus problem wasn't too hard to get around, if you search around you can find ironhide or The Bumblebee Project which solve most of the issues (but don't support swapping between the cards).
The trackpad was easy to get working again, just I haven't been able to find any way to get the multi-touch functionality working.
Probably the worst problem I've noticed is the wireless problems. First of all, the bluetooth and wireless are hard to separate on this laptop. If you disable the bluetooth, the wireless doesn't work. Also on my school wifi I have a sketchy connection at best. Been trying to find a way around it but still haven't completely solved it. The network sometimes takes a while too connect, sometimes won't connect, and frequently drops connection.
But this seems to be a router dependent problem due to the fact that at my apartment the wireless works perfectly. So the odds are you'll be unsatisfied with the wireless till a fix for this problem is found.
Other than the wireless, I've been completely happy with this laptop!