While I have no knowledge of Exchange, I use (and rely on) it daily. My co. has something like 10,000 UK Exchange/Outlook users each with a 100MB quota spread across (I believe) 8-10 servers.

I'd bet though that most of my colleagues would (if asked) complain bitterly about periodic outages, having to log out of Outlook for scheduled hardware work etc. I often (once/fortnight) arrive in the morning and unlock the Win2k console to find Outlook has hung only to find that I hadn't bothered to read the mail from IM telling me to logout the evening before because of scheduled maintenance.

In 5 years only on one occasion have I ever heard about people losing emails - a server failed (RAID controller I believe) and some people lost about 3-days of sent/received email, myself included.

I guess what I'm really trying to say here is that I believe I gain a lot of productivity from Exchange/Outlook with it's Calendar, meeting requests, task scheduler, document tracking etc. that I would find it hard to re-adjust to a life without it. Maybe there ARE better solutions out there but Exchange works sure well for me too