I have a Django app in its early stages using 1.3, would it be a good idea to just transfer it over to 1.4? The only third-party app that it is using is django-registration...
Try it and see - if you're not using virtualenv - you should be. If it doesn't seem compatible, just install 1.3 back.
The main problems I ran into when upgrading were with the new timezone support, but it was easy to just disable it (set `USE_TZ = False`) until I have a real need for the feature (and the time to fix the issues it causes for current code).
I'm using a lot more (including django-registration) with 1.4, go ahead.