I use it for work with my Google Work account, and on my personal machine with my imap provider. Aliases, PGP, autobcc, virtual folders + labels, calendaring, tasks, multiple accounts, ...
I use imap custom labels (flags) + virtual folders and also use imapfilter to automatically add labels based on conditions (can write more complex stuff using lua). I really wish more clients supports imap custom labels. I am a zero inbox person, so its really important to be able to quickly and easily label things.
Invitations + Calendars all work well which is important for work.
As a heavy emacs user, I have considered emacs+mu4e. I think it'd work fine for my personal/side business, but I just don't think it work well for my work, as calendaring is critical.