Apple fixed most of the Bluetooth connectivity problems in the 10.4.5 update, leaving just one unresolved issue, wherein you can't send a file from the phone to the Mac. A workaround was posted on the Blue Mint blog.
Essentially you need to "kick-start" the Bluetooth transfer by switching tabs in Bluetooth's Preference Pane. Open Bluetooth's prefs, click Devices, start the transfer, then click the Sharing tab. It sounds silly, but the method works for me.
[robg adds: I added the 'super summarized' description of the method above, as it's my intent that the hints found on macosxhints should be able to stand alone if the source site ever goes away. There's more detail in the linked page, of course, where they also note that the original workaround came from this entry on rasterweb.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060220183753841