Is there a convenient way to delete them other than hitting the BB button and two clicks after that for each one? It would be nice if there were a way to mark several of them for deletion (like you can in Gmail on a computer, for example), or at least set up a shortcut key to delete, but I haven't figured either of those out yet.
The delete key on the keyboard works for individual emails (and the enter key right below it for the delete/cancel dialog is faster than reaching for the trackpad). You can also go to the date header for a list of messages and choose "delete prior" to delete all emails before that date.