On the pearl, if you want to copy a phone number into your address book, and not have it appear as a work number:
From the call log, select the number, from the left key menu, select copy phone number. Then go to your address book, create a new entry, and scroll down to the mobile number section and paste it (using the same menu key).
As steve said, there is no way to not have it default to work number. Yes, a little annoying. But I guess it's the sole caveat compared to everything else the device offers.
Also, the BB pearl (and I'm assuming the Curve as well) does not by default put dashes between the area code and number. I believe this is because when you receive the call, it just comes up with the numbers alltogether (ex: incoming call from 5165551212, instead of (516) 555-1212). This isn't a problem for most, just in my case, since I transferred everything from my old Treo, half the numbers in my phone are in proper format, and half aren't
