Blackberry + Mail.app + Gmail = ♥
Before I bought my Blackberry 8320 I used to have Apple’s Mail.app connect to Gmail through POP. Obviously this is very cumbersome because I would have to periodically login to Gmail to clean out the emails I had deleted from Mail.
Enter the Curve. This smartphone has the option to delete emails from the server when they are removed from the phone. Add to this the fact that Gmail has since gone IMAP and you have a triad of email portals that are all synchronized.
Step 1. Configure your Blackberry
While in your messages, hit Menu and navigate to Messages Options -> Email Reconciliation -> Delete On: Mailbox & Handheld

Step 2. Configure Mail.app for IMAP Gmail
Add a new account and set Account Type: IMAP and fill in the rest of your gmail credentials.
Step 3. Enable IMAP in Gmail

Now, when you delete an email from your phone it will be removed from Gmail and Mail as well. (If you delete it from Gmail or Mail it will delete from the Blackberry but only after several hours when it reconciles with the server.)