If you are using IMAP and migrating from OUTLOOK 2007 or earlier be aware now that DELETE actually DOES DELETE directly in OUTLOOK 2010..
Outlook 2007 puts a line through items which you then delete by selecting the PURGE option. There's no PURGE option in OUTLOOK 2010.
I prefer the outlook 2010 method -- it behaves like POP3 delete.
However if you are used to the OUTLOOK 2007 then take care of the difference in behaviour.