For one and a half years, I have been keeping my eyes on the git community in hopes of making the switch away from SVN. One particular issue holding me back is the inabilit
Subversion has locks, and they aren't just advisory. They can be enforced using the svn:needs-lock attribute (but can also be deliberately broken if necessary). It's the right solution for managing non-mergeable files. The company I work for stores just about everything in Subversion, and uses svn:needs-lock for all non-mergeable files.
I disagree with "locks are just a communication method". They are a much more effective method than push-notifications such as phone or e-mail. Subversion locks are self-documenting (who has the lock). On the other hand, if you have to communicate by other traditional push-notification channels, such as e-mail, who do you send the notification to? You don't know in advance who might want to edit the file, especially on open-source projects, unless you have a complete list of your entire development team. So those traditional communication methods aren't nearly as effective.
A central lock server, while against the principles of DVCS, is the only feasible method for non-mergeable files. As long as DVCS don't have a central lock feature, I think it will keep the company I work for using Subversion.
The better solution would be to make a merge tool for all your binary file formats, but that's a longer-term and ongoing goal that will never be "finished".
Here's an interesting read on the topic.