At the moment, the Duty Finder can pull from any server and that's great for finding groups quickly to enter instances. That said, I think it's a shame that we can't re-establish parties which we find particularly excellent.
Today, I went into Brayflox's Longstop - I was farming for Cavalry Armour, but we had an amazing run through the dungeon which everyone in the party enjoyed. The only problem is that we were all from different servers - I'll probably never party up with any of those players again and I can't even add them to my Friends List, and this is despite a mutual desire from all of us to have that option. I think it's a shame that you can't make friends through dungeons.
That's why I'd like an option to limit the Duty Finder to players from your own server. Sure, it would take longer and sure, the parties you go with may not always be that great, but it would be nice to have the option to friendship-build through dungeons as is the way in most MMORPGs.