I mentioned a while ago that I use Google Apps personally, partially as a way to evaluate it but mostly as a way to get all my e-mail into one place.
Regardless of the problems I had with Google Apps, I eventually moved all of my work e-mail back to my work account, and split everything back up. Obviously, the question of why I’d go back—particularly since Google Apps has fixed some of the bigger (i.e. non e-mail reasons) why it sucked for my purposes, including the integration with other Google tools (except YouTube, grumble grumble), and the Gmail mobile client finally being able to send from multiple accounts.
The reason is simple: at work, we maintain an in-house Zimbra setup, and if Zimbra sucks, then those of us who are responsible for it need to know all the ways it sucks, and figure out how to make it sucks less. I’m not saying that Zimbra sucks, of course (though it certainly has it’s moments), simply that if you’re supporting a tool over for someone else to use, you had better be intimately familiar with it. If I’m not using it, then there could be some weird issue that we’re not monitoring for, and we’ll get bitten by it.
This is, honestly, more often a problem in operations than development: on the development side, we’ve all run into APIs or toolkits that were so bad it was inconceivable that the designers actually tested them, but few people actually develop those APIs. In operations, it’s not entirely uncommon for IT to carve out special access for themselves (after all, they have root anyway), and forget about the limitations of the unprivileged user.