When you've got a browser or two and a Linux VM running, finding the extra 500Mb for an IDE can be rather taxing. I've tried IntelliJ, Eclipse and NetBeans. Always end up coming back to MacVim, saving a few hundred megs of RAM and not really getting any significant hit in productivity.
I was trying out PyCharm the other day (IntelliJ's Python IDE) and it was unable to keep up with my fingers. The text was lagging a I was typing it in. What was I getting from the IDE? Debugging? I know my way around pdb, haven't got time to work out how the IDE fucks that up. File navigation? I've got Ctrl-P. Changing between project configuration? Meh. Got Vagrant for that kind of thing anyway. That leaves autocomplete (can take it or leave it. Not bothered.) and refactoring (mostly I use Python and Ruby at work, so mostly it's a shit show anyway IDE or not).
Even on Scala projects, I've gone in thinking "IDEs are the answer" and ending up back in Vim after a few hours of flailing around trying to get the IDE to talk to the compiler.
Agreed on Mercurial though. I like Git, I like Mercurial. Both have upsides and downsides. More important is that we are finally moving away from centralised VCS.
On the other hand I haven't seen any good free Python IDE-s (like Visual C++ is for C++) and you are sometimes forced to use pdb for the lack of a better option (Python Tools for VS are decent but took me a lot of time to setup properly and I didn't like the workflow).
That said, the lack of good tools doesn't mean the old ones are good, only that the language lacks good tools, mostly because people get used to the stone age tools. And sadly that is the case for a lot of programming languages.
The RAM thing still bites. When I get a new laptop in a year or so, I'm going to go all out on RAM. :)