The synchronisation experiment has not been a great success. As many might have predicted events and contacts are uploaded / downloaded in some apparently random manner, causing everyone's birthdays to be duplicated every time I sync Plaxo, and contacts on my phone to be deleted by ActiveSync. It's infuriating that this problem still plagues PIM software.
Anyone I've met in the last three months has been wiped, including the electrician who's currently rewiring my flat, in my absence!
I do however, have a fairly complete set of info on Plaxo, sync'd to my home and work desktops. Adding in the Smartphone causes a few headaches, but things are definitely better than they were.