Google's view on this move is that there are open protocols like IMAP, CalDAV and CardDAV that can do all of this syncing just as easily. IMAP is universally supported, so syncing your Gmail should stay just as easy as it has been. The trouble is that only Android and iOS support CalDAV and CardDAV. There has been some indication that BlackBerry 10 will support them as well, but current BlackBerry devices don't.
The big trouble, not surprisingly, is with Windows Phone, which not only doesn't support CalDAV or CardDAV, but also notoriously doesn't have the support of Google itself building apps for the platform.
Of course, that all said, this won't really change much if you're already a Google Sync user, because the End Of Life plan for Google Sync is currently to stop offering it as an option for new free accounts as of January 30th, 2013. If you are signing up for a paid Google Apps account, you'll still have access to Google Sync.
So, if you think there's any chance of you switching to Windows Phone or BlackBerry, you may want to sign up for Google Sync right now, so it keeps going after January 30th.