StackOverflow tagged questions: Django 36000+, Flask about 3000 (Flask 675 + SQLAlchemy 1880 + Jinja2 376)
Google Groups: "Django updates" 35864 topics, "Django users" 37333 topics, Flask (no user groups)
PyPi packages: Django 2539, Flask (no classifier for flask but somewhere around 260 search results for 'flask')
IRC: #django usually has 500-600 in channel at all times of day. I can't connect right now for exact numbers for flask (assuming there is a channel) but other frameworks like Pyramid are probably equivalent and less than 100.
Now, except for IRC these numbers don't judge current momentum... but they still give a good indicator on community size. For example, in all these areas plone/zope numbers beat django but clearly momentum is towards Django when comparing the two.
Not they are not related at some level, but this evidence is irrelevant.
Agreed on last parapgraph. Everybody needs to make sure their preferred environment matches their requirements. Django might be moving faster than Plone/Zope, but if you are a big enterprise looking into content management, the question is almost already answered.
http://webchat.freenode.net/?channels=pocoo&uio=OT10cnVl... Flask IRC Channel
groups.google.com/group/pocoo-libs Flask Google Groups
twitter.com/PocooProjec Flask Twitter