I host my email through a Google Apps account. I have very few complaints about the BlackBerry integration.
Using the Enchanced Gmail Plug-in gets you a lot of the Gmail functionality on the BlackBerry. Unfortunately synchronization isn't fully two-way.
The current version of BIS allows you to sync your contacts. Because of how Gmail handles addresses, contact addresses all get thrown in the Address 1 field on the BlackBerry, but they appear fine when viewing the contact. You also cannot sync contact pictures. Any pictures you have on the BlackBerry will be removed. Pictures are left alone in Gmail.
Calendar sync through BIS is still an upgrade or two away. For now you can sync your calendar using Google Sync (it can also do contacts if you don't want to use BIS for that). You can download as many of your calendars as you want (sports schedules aren't available, I'm not sure if anything else isn't either), but you can only write new events from the BlackBerry to one calendar (you can always change which one if you need to add to multiple). My only real complaints are that you can only sync 4 weeks back and 24 weeks forward, and that recurring events appear on the BlackBerry as individual events.