I've looked into it, but haven't really done side-by-side comparisons in use. I've read a lot about Bazaar and touched it a couple times, though.
It seems to be slower, more prone to issues, and more prone to regular changes in the interfaces for, and implementations of, basic functionality. It also does not seem to really add anything that you don't get with Mercurial. Furthermore, I'm not as impressed with its code hosting options as I am with the options for Mercurial -- which include BitBucket, ShareSource, and Google Code, among others.
While I'm at it, I like Merucrial's C and Python codebase more than Bazaar's C, Pyrex, and Python codebase (or Git's Bourne Shell, C, and Perl codebase for that matter). While I'm a fan of using the right tool for the job, and thus have no problem with a codebase that's split between a high performance language and a higher-level dynamic language (say, C and Python), I'm not a fan of unnecessarily diversifying the implementation languages (Why use Bourne shell and Perl? Why use Python and Pyrex?). I know that Pyrex is basically an extension to Python intended to ease the process of writing parts of modules in C, but it still seems like an unnecessary layer of abstraction to me.
I am not yet sold on the idea that we actually need folders in and of themselves to be treated as first class objects, either. I guess it feels more "natural" that way, but it's just not really necessary, I think.
As for TortoiseSVN -- I used it a little bit years ago, and did not really have problems with it, but I wasn't trying to use it with another VCS at the time, and did not use it really heavily. Basically, my major VCS use has always been in a Unix environment.
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