managing multiple contact sources as gmail contacts
KADlancer - check out http://www.fullcontact.com. (Full disclosure: I work for them, so I'm a bit biased. But the issues you mentioned are exactly the issues we're trying to solve).

We currently have a web app in private beta that pulls in contacts from various Google Contacts/Gmail sources, as well as Facebook, Foursquare, LinkedIn, Twitter, etc. It then adds social profile data to each, normalizes &amp; de-dupes them, and syncs them back in real-time.

Within the next month we plan to roll out our public beta, which will support the linking of all of the above sources - meaning you can unify contacts across all your social networks/Google accounts and have all your contacts in one place, automatically up-to-date. Because we offer two-way sync in real-time, changes made in Google Contacts sync to FullContact, and vice-versa - meaning that your data is your data, and stays where you want it (no walled gardens).

Again, I work for them, so you'd probably be right to take what I'm saying with a grain of salt. But based on what you posted, it looks like the FullContact Address Book will do almost everything you're looking to do (with the possible exception of Xing, which is currently not supported, but on the roadmap). I'm not aware of any other app out there that does quite what we do, save Smartr - which it sounds like you've already tried.

Good luck!