I can speak for the Palm Pre, I do know that MarkSpace has released a "Missing Sync" for he Pre to sync to the Mac since Palm didn't develop a sync method for the Mac and the Pre won't sync with the older Palm solutions.

While it's true that if you have multiple notes on your contacts they won't sync to the iPhone (nor will they sync to the Palm Pre for that mater), that's been the case for syncing as long as I can remember and is a limitation of the tools we're given to sync out to. Sync services has a schema that only supports a single note for contacts, as does the iPhone and AddressBook.

Speaking from my own experience syncing to the iPhone, 5700 contacts may be a bit taxing on the phone. It will handle the sync, but you might find it difficult to use and very slow, the interface just isn't designed to deal with a lot of contacts.

The bottom line is that Now X syncs with Apple's Sync Services, so any device that also syncs with Sync Services (even through third party solutions like MarkSpace or PocketMac) should be able to get your Now X contact and events. Not all the data will be available, we're limited by what those other devices and/or programs will support, but most of the pertinent information is shared.
Sean Boiarski
Product Manager, Now Software