Yes -- I write ~95% of my python code in 3, and scrapy is the only library I commonly use that doesn't support it. Here's a listing of package compatibility: http://py3readiness.org/.

In most cases, yes. There are libraries that you might want to use that don't support it yet but the vast majority do. Personally, I'm anxiously waiting for Fabric 2 which has been pending for a long time. This is a good resource for figuring out whether the libraries you need are ready: http://py3readiness.org

Unfortunately I'm stuck on 2.7 until Google updates App Engine

It's been ready for prime time for the past 3 years.

Py3 has been prime time for a while now. Been using it full time since Py 3.3 for all my work and I haven't had any issues with it. There were some external libraries such as the library given by a twilio competitor that were incompatible, but easily fixed (almost exclusively, encoding issues).

Although, I still find myself running tests and cursing at the fact that I keep writing print "string" without the brackets :D