> I also don't understand what usability complaints users would have, since for the most part, they access it through a client such as Outlook.
Disappearing & reappearing emails through outlook. (And occasionally disappearing and not reappearing; Had something to do with ActiveSync and outlook open at the same time, but I never quite managed to exactly characterize it). Despite exchange's hyper configurability, those disappearing and mostly reappearing messages did not have anything in their logs different than anything else.
Also, search was abysmal.
Larger mailboxen (3-4 GB at the time) caused huge slowdown, and people were moving stuff to local (though, not backed up!) archives sorted by quarter, so that the recent year or so would perform reasonably.
> But you're comparing a service in 2012 to one in 2006.
I'm comparing Exchange at 2006 (I think it was Exchange 2005? but it might have been Exchange 2003; It was the latest available at the time) to Gmail at the time. Everyone preferred gmail to outlook web access, and most preferred it to Outlook as well (for tags, search and predictable behavior).
I'm sure Exchange has improved since, but so has gmail. What can exchange 2013 (or exchange 2010, which is the recent battle-tested version, unlike 2013) do that that Exchange 2005 couldn't?