Before the update I could only get email, both POP3 and IMAP, by doing a manual refresh and then it took forever. I'm also using K-9 and after the update nothing changed so I uninstalled and reinstalled K-9. What a difference! Now I get email quickly and have it on a 15 minute poll cycle and everything seems to be working great.
I turn off my phone at night so I don't know what's going on there. However, when I turn on my phone, usually around 6 am, any accumulated email is brought right in with no problem. Maybe the uninstall/reinstall process will help.