Though syncing between different accounts (my gmail account + my google apps account) is not trivial. There are some decent apps on the google apps marketplace, but none of them work as seamlessly as single account syncing. But I wouldn't call it an "unsolved problem" in any way.
Are you using this with Android?
I stopped bothering after my 2.3.x phone insisted on "syncing" in one direction only from Accounts --> Phone and reverting any updated numbers on my phone.
Can anyone explain in simple terms why this is so?
Still though, it was pretty nice. I still remember trying to figure out how to develop games for it. My household didn't have the internet at the time and my access to the library was limited (we lived on a farm), so in the end I was just a 13 year old who had a machine with all of his classmates' names and birthdays organized on it.
What a time to be alive.
long story short, they complete fucked up the companies MS Outlook bases CRM system with one address book HotSync© action - by one employe.
That employe was me (I was just the first to push the HotSync© button...).
there was a backup of Outlook of course, sadly the backup could not get used to restore the CRM (don't ask...)
about 20 people were typing in address data for the rest of the week.
i now have 5 Sony CLIÉ at home, i hope the will be worth something sometime.