I love mercurial, but you don't get quite the benefit of `git add -p`, because mercurial has no staging area. If you quit out of `git add -p`, you still get the benefit of having whatever you added staged. In contrast, if you quit `hg record` (because you wanted to change something before committing), you have to re-record all the changes you wanted.
if you use mercurial's mq extension you get the equivalent of a staging area if you really want one[1]. There is qcrecord to get git add -p functionality with mq.
Personally, I have stopped using queues and I use rebase and histedit extensively now. I see no need for patch queues or a staging area when you can edit and rearrange commits easily.
"Extension" in quotes, because it comes with the Hg installation -- it's just one of those advanced things disabled by default.