This is a little annoying. Every time I go to delete a message, I get a dialog box asking me if I want to delete it on the handheld. In every account I have "Confirm Delete: No" in my settings and Wireless Reconcile is off. Why is it still giving me a dialogue box? I get a LOT of email to my work account and I like to delete them quickly. (All of my email is stored in other places so I'm not worried about accidentally deleting emails.)
If you go to Messages > Options > Email Reconciliation set the Delete On to either Handheld or Mailbox and Handheld. With my Confirm Delete set to No in the General Options and the aforementioned setup, my BIS mail is deleted without any prompts.