I've found Google Apps sluggish when it comes to bulk actions. Even using its own tools to migrate from Exchange, it's slow.
I admit, more and more I've stopped using a local MUA and switched to using the web interface a lot of the time. When I have had need to grab old user's emails and roll them into a "past employee's mailbox", it's been sloooooow and I've left it running in a background process, and had to do a couple of passes to ensure that all the emails were captured.
Would be curious to see, however, what people do suggest for an MUA these days..
I mean, Outlook SUCKS BADLY for IMAP (want to purge the download cache? Delete the account and add it again :-/) and GSSMO has "Personality"..
Evolution was horrible when I looked at it last (maybe it's improved?) and scattered files throughout the filesystem..
Sylpheed is very low-fi and only single threaded..
Is Thunderbird getting active development these days (did I misread awhile back it'd been kiiiinda orphaned at some stage?)
I dunno, it feels like MUAs haven't been getting a lot of love of late.