nathan: are you up to date with the latest Outlook 2013 updates?
a bunch of IMAP synch breaking bugs were fixed in the September release
and performance improvements coming in SP1 which is shipping shortly
I'm using Outlook 2010 and did see a bunch of updates the other day (quite a few office ones), but IMap is still rather un-functional (as to say how it works on the IPhone for example). Am using 8.1 (ok preview) and would argue about your definition of the word 'improvement' on the principle that I still can't send email via Hotmail due to a certificate error (I must point out that I am waiting for the release to see if we get a working set of certs before registering this as a defect).
I would move to Office 2013 in an instant, were it not for the slight issue of only being able to install on one device (whereas Office 2010 allows me to install on desktop and laptop) and the privilege of paying more for not being able to do so - and I have no desire to use cloud anything (or Office 365). :)