One feature I like in Perforce (which Subversion doesn't have) is the ability to have pending changesets. A changeset is, as with subversion, something you check-in atomically. Pending changesets in Perforce allow you to (1) group related files in a source tree where you might be working on multiple things at once to ensure and (2) to build a change description as you go. In a large source tree this can be useful for separating chunks of work.
There are other little things, like not being able to trim the check-in filelist when editing the check-in message. For example, say you have 10 files checked out scattered around the Python source tree and you want to check 9 of those in. Currently with svn you have to manually specify those 9 to be sure to not include the remaining one. With p4 you just say to check-in the whole tree and then remove that one from the list give you in your editor with entering the check-in message. Not that big of a deal.
[Martin v. L?wis on Perforce]
The biggest disadvantage, to me, is that few people know how to use it (myself included).
Granted. For that reason and for a couple of others I mentioned (SVN will probably work better for offline and distributed developers) I think Subversion wins over Perforce. That is presuming, of course, that we find Subversion to be acceptibly stable/robust/manageble.