There is something though that stops me from using it as a daily driver. In the DP1 you cannot use your standard iCloud App Data. For example, 1Password cannot read the iCloud files, and every other app has also the same issue. iCloud data created from DP1 can only be read from DP1 and at some point these data will get deleted from the iCloud servers, so you have to be careful. Also my Mail rules are not there, as also my mail signature. The Developer Preview 1 shouldn't be used productively.
There are also many compatibility issues (understandably). VMWare Fusion doesn't work for example, Final Cut has issues, etc.
I understand the urge to use the new UI (which looks great on Retina but not on non Retina Macs), but I believe we should be patient.