I use Subversion a lot because a lot of employers use it and I had a lot of experience with it in the past. It fixes many of the glaring flaws in CVS. The moto of Subersion used to be "CVS done right", but Linus Torvalds joked that there is no "right" way to do CVS right and now I agree. Subversion is useful and it is not the worst thing in the world (CSV), but it is fundamentally and conceptually broken. It's easy to use git in a similar workflow as Subversion (centralized repository) and even handicapped like that it outperforms Subversion and is just as easy to use (even easier and better when you consider merging). So... I am a convert to git.
Subversion has flaws and limitations, but it's better than CVS and it's cheap. The low price doesn't reflect low quality or lack of support. Subversion does not do distributed version control and merging is bad; although, a third-party tool makes merging a bit more tolerable. It is also difficult to automatically generate reports that graph changes. The problem is that all the commercial offerings are very expensive. ClearCase is expensive to buy and very difficult to maintain. It is complex. Perforce is probably better, but it is also expensive. It's hard to beat free!