Not so long ago I decided to play with launchpad - site for open source collaboration. It is built around decentralized Bazaar version control system that reached version 1.6 in its development up to this moment. I read that centralized VCS are bad and DVCS are good, but never had enough free time to check this in practice and finally..
The first thing I liked in Bazaar is that it is written in Python - that means that bugs can be found and fixed rather easily. This was also the thing that I disliked, because standalone bzr distribution includes Python and takes 14Mb and package for installed Python distribution doesn't add bzr to PATH
Accessibility. I often work through tunnels, proxies, firewalls and other stuff that kind people tend to put here and there in each Local Area Network. Not only I have to deal with them myself, but sometimes also need to teach others. In SVN proxy settings are stored in documented configuration file called 'servers'. In Bazaar there is no such file and all configuration is done with environment variables and Python settings that are not documented. To use Bazaar through a proxy - set environment variables:
These proxy settings are rather common for linux/unix machines, but cause particular pain with windows machines in a domain. If SVN is able to transparently authenticate against domain proxy without asking sensitive passwords then Bazaar lacks such feature and needs another authorization proxy server (NTLMAPS) middleware.
Usability. In general distributed version control systems should be better than centralized ones. A lot of articles and tutorials describe the theory very well, but in practice there are many things is are not that brilliant. For example, I needed to fix stubborn DevPak plugin for Code:Blocks that didn't want to install one specific version of a curl library. In SVN I would do a partial checkout, make modifications and upload patch to the forum. Not very convenient. In Bazaar I would have to make a branch of the whole Code::Blocks repository, start patching plugin and then merge the whole branch back. But branching the whole repository is an overkill for such little plugin and you can't make a branch out of subtree in Bazaar. More then that - Bazaar doesn't even allow to export subtree of repository. Download either the whole thing or nothing. Not too effective, especially when the traffic is 0.02 cents for Mb.
So, I manually created directory structure for the plugin similar to existing project and started a new Bazaar repository from scratch. After a couple of revisions I released fixed plugin for stable Code::Blocks and would like to switch to latest development code and merge changes made to plugin in trunk into my version. Again, Bazaar disappointed me. I knew that SVN won't allow merging with different repository, but at least I could grab files from the source tree and merge them manually. Bazaar didn't allow me even that. With almost 100 commands it just couldn't export some files.
It may be that Bazaar is a good system for some small projects, but in my case it appeared unwieldy and too expensive even being open and free.