I postulated that more detailed, longer commit messages are good for others to understand the changes you made in the future. However with git you can easily write a more detailed message at a later date (by re-basing, altering commit, more details in the merge message, etc) before the code is pushed or submitted as a patch – and only if its really needed. This means you don’t have to interrupt your local workflow which allows you to code fearlessly. SVN and CVS made commits a heavy weight process that required more care which led me to be biased in this area at the time.
I do believe it is import to have a good model for your git workflow though, I’ve been trying a work flow publish by Vincent Driessen and while its a bit of overkill for an individual project, the steps are easy to remember and well defined. Only thing I’m not sure of is if merging without fast forward will cause problems over time, but in the short term grouping commits and keeping that knowledge is useful.