Yeah i have fantasies of having my own email server and stuff but the spam detection is probably the 3rd thing that would have me crawling back
I'm running my own mail server for longer than I'd like to admit, but not for my critical/key email addresses. Looking at the spam filtering I get in Gmail and knowing my endless fights with spamassassin and DSBLs I know I could never achieve that.
The only upside of having an actual mail server is the ability to say "this is incorrect, no one ever tried to send an email to this address/from this IP" or custom 55x messages.
I have run my own mail server for years and I rarely see spam. I'm running a classic Bayesian filter as outlined in the legendary PG post "A Plan For Spam" and it works very well. I don't really get all the fuss about this issue. When I do see a piece of unclassified spam I simply classify it and continue. For me this is a far better tradeoff than having all my most private mail on some bigcorp server where any nerd can rifle through it.