I just converted from Treo to Moto Droid and it was easy thanks to the tips in this thread.
For the calendar I used Shred's converter at
http://pdbconverter.shredzone.org
Shred's converter allows you to control the date range you pull so you don't overwhelm Gmail's Calendar as it tries to upload your stuff. Excellent converter! Thanks, Shred.
My contacts required some manual effort in Notepad (I have > 1000) but not too much. From Palm Desktop I exported my contacts as Vcards (.vcf). Then did a Search & Replace on:
Replace =0D=0A with a comma or special character of your choosing.
Replace X-Palm-Custom1: with NOTE:
Replace EMAIL: when it stands alone with EMAIL;HOME;INTERNET: or EMAIL;WORK;INTERNET: as the case may be.
Then I imported the final contact file into GMail without trouble.