I use the heck out of the appts and tasks - appts are "things that I have to physical participate in" (phone call, lunch) and tasks are "reminders". I would not survive long without those. I use Trello but only to manage a small team of tasks.

You said, "The only thing I'm missing is better attachment management" - to me, the worst part about Outlook is the search functionality. It's just awful IMO. I can deal with the crappy attachment handling/saving/etc but when it takes a week for the "Instant Search" thing to index my 2gb Outlook file, I get pissed haha