What do folks here see as the relative strengths and weaknesses of Git, Mercurial, and Bazaar?
In considering each of them with one another and against version control systems like SVN and Perforce, what issues should be considered?
In planning a migration from SVN to one of these distributed version control systems, what factors would you consider?
Mercurial and Bazaar resemble themselves very much on the surface. They both provide basic distributed version control, as in offline commit and merging multiple branches, are both written in python and are both slower than git. There are many differences once you delve into the code, but, for your routine day-to-day tasks, they are effectively the same, although Mercurial seems to have a bit more momentum.
Git, well, is not for the uninitiated. It is much faster than both Mercurial and Bazaar, and was written to manage the Linux kernel. It is the fastest of the three and it is also the most powerful of the three, by quite a margin. Git's log and commit manipulation tools are unmatched. However, it is also the most complicated and the most dangerous to use. It is very easy to lose a commit or ruin a repository, especially if you do not understand the inner workings of git.
What do folks here see as the relative strengths and weaknesses of Git, Mercurial, and Bazaar?
This is a very open question, bordering on flamebait.
Git is fastest, but all three are fast enough. Bazaar is the most flexible (it has transparent read-write support for SVN repositories) and cares a lot about the user experience. Mercurial is somewhere in the middle.
All three systems have lots of fanboys. I am personally a Bazaar fanboy.
In considering each of them with one another and against version control systems like SVN and Perforce, what issues should be considered?
The former are distributed systems. The latter are centralized systems. In addition, Perforce is proprietary while all the others are free as in speech.
Centralized versus decentralized is a much more momentous choice than any of the systems you mentioned within its category.
In planning a migration from SVN to one of these distributed version control systems, what factors would you consider?
First, lack of a good substitute for TortoiseSVN. Although Bazaar is working on their own Tortoise variant, but it's not there yet, as of September 2008.
Then, training the key people about how using a decentralized system is going to affect their work.
Finally, integration with the rest of the system, such as issue trackers, the nightly build system, the automated test system, etc.