* I am hacking on some bit of code, so I set up a Perforce branch. While I'm at it I notice some ugliness and want to refactor it. I could make a new Perforce branch and put it there and then do some horrible merging apparatus but it's complicated and they live forever and it takes me out of the flow state, so I just make a commit. It is now very difficult to extract that commit from its context so that I could apply it independently.
* I make a mistake on a commit that is on a private Perforce branch, or maybe I did something out of order. The Perforce way is "you shouldn't have done that, then." and so my commit logs are full of "fix stupid typo" type commits that are basically just noise.
* I forget to add a file to Perforce and nothing tells me about it, ever, until we get to testing (or sometimes to production!) and Puppet won't run because it can't find some file <foo>. This is fixed with the 2012 betas and p4 status, but those require a server upgrade (because the p4 client is a thin wrapper around what the p4d server understands) and that isn't in the cards yet. This alone is enough to make me want to use git-p4 for everything.
* You can really tell that Perforce is built around a file system of RCS files sometimes. While it has atomic commits, many, many operations are based on individual file revisions (labelling, cherry picking, merging). This leads to the following:
* Cherry picking in Perforce is hard, because it's hard to get handle on the content of a changeset, as opposed to individual upticks in each of the files referenced. It can be done but it is a lot of effort, way more so than in git.
This is not the entirety of my complaints about Perforce, by any means, but they're the most visible UI limitations compared to what I'm used to from git.