As a brief interlude to my never ending series of blog posts about migrating from Gmail to FastMail, I'll quickly note that:
a) Gmail has some problems when used as an account in the Mail app of Mac OS 10.9 (Mavericks)
b) FastMail also has some issues when being used with Mail on Mavericks (these would seem to be due to changes Apple made)
So on the one hand, the former news might encourage more people to move away from Gmail but the latter news item means that Apple's Mail app needs some fixes before being ready to work with FastMail under 10.9 (of course, web access to FastMail is unaffected). This is making me consider waiting a little while before upgrading to 10.9.
Update: 31st October
Turns out the 2nd item above was not FastMail's fault and was an issue with a particular user.
Update: 4th November
Marco Arment's piece on the wider issue of Gmail not adopting standard IMAP protocols is well worth a read.