had exactly the same problem with the version prior to current release and was unable to solve it so just live with it.
it is a complete pain (and still exists in new version). I collect 9 pop3 accounts into 1 inbox and have 2 minute intervals between send/receive schedule. Have altered this to 5 mins and 10 mins (as recommended by michael) but this didnt solve.
The hang lasts anything from 30seconds to … well i wasnt patient enough to find out but is over 10 mins at least. Have watched activity monitor and entourage has upto 63% cpu and drops down to under 1%, spamsieve also minimal on cpu usage the machine is just hanging there and it also adds a time lag to anything else you are trying to do on the machine at the same time.
The only way i have found of getting things working again which can take upto 20mins by the time you’ve done everything is relaunch system, and disable send/receive schedule - then collect each account in turn. Occassionaly you will hit an account that hangs and it’s then forcequit and try that account again. Complete PITA. Then check in each account settings and download all messges for this account to ensure nothing is stuck. Empty the junk, delete the trash and (not sure if this helps but i do it) move everything out of inbox and into archive folders or a folder within inbox. Everything is then empty. Quit entourage, relaunch, reactivate schedules and it all seems to work again (for about 2 weeks) without hiccup. Hardly a fix but this is what I have to do to get things working again.
I did however find that the corpus was also getting too big the other day and this was causing a very similar slowdown - could be related.
Finally, and I have only discovered this since using my workaround above. If you force quit spamsieve (which sometimes releases the hang too!!) and then relaunch it, it isnt actually active despite being open in the dock i.e. after force quit spamsieve you must restart machine for it to actually be active.
well hope this sheds some light I am coming up to my two week limit and am starting to notice a slowdown with send/receive - process so guess its coming up to fix time again.
sorry this is not technical but it works for me!!