I have been using Google Apps for my domain for a few months now, and by and large, I have been very satisfied with their service. But all that aside, there is one big problem that I have with my Google Apps accounts - that I can't use them in any other services aside from those setup for my domain.
If I want to use Orkut, the new Blogger Beta, or even the Google Toolbar's custom features, I still need to use my old G-Mail account. Granted, this isn't a major inconvenience, but I would much rather have an opportunity to do this with just one account, and just one password - it would make things a lot easier.
Are you listening Google?