Git-using colleagues mainly, who may need to work on your machine for one reason or another (imagine git as the standard SCM and pair-programming, your using a different "porcelain" only works as long as your colleagues can keep using the standardized tool).
It'd also feel a bit less hack-ish than my current hg-git setup, and it would probably work correctly with http git repositories (I believe hg-git will support them once Dulwich 0.8.1 is released[0], but I've no idea if — and when — that'll happen, not to mention the issue will rise its ugly head again if git adds more protocols in the future)
