The list of new features is a little underwhelming. Multi-threaded debugging and the unit testing tool (only supporting unittest -- does anyone still use that old module anymore?) are nice but I don't see myself paying to upgrade from 2.1 yet. Now if they could get the GUI to keep up with my typing in Windows, I'd pay for that... I guess this is a sign that Python IDEs are nearing maturity; Komodo 4 didn't have any earth-shaking new features either, at least as far as Python was concerned.
(Personally I think someone should start supporting django/genshi/mako templates already. Maybe in 3.1, guys?)
Following ActiveState's lead, Wingware has also released a completely free version, Wing IDE 101. The main difference is that where the most essential feature Komodo Edit leaves out as an incentive to upgrade is debugging, Wing IDE 101 includes the debugger but omits code completion. Wingware also continues to offer the low-cost Personal edition.
But the really big difference between Wing IDE 101 and Komodo Edit is that you can freely use Komodo Edit for paying work. Wing IDE 101, like Wing IDE Personal has a no-commercial-use clause. (Komodo versions compared; Wing versions compared.) I'm still of the opinion that at $180, Wing Professional will pay for itself in short order, but for the hobbyist, Komodo Edit is very compelling. I've been using it myself for TCL and XML editing for several months now and it's a nice little IDE.
Too bad Komodo's emacs bindings continue to suck balls -- I mean, it's one thing to not implement fancy things like a minibuffer or kill ring, but if you can't even get C-W (cut) right, there's not much hope. Users contributed much-improved Emacs bindings to the ActiveState bug tracker way back in the version 3 timeframe. I guess ActiveState just doesn't care.