On current form I can't think of a better LB out there. Evra has been the stand out player in that position over the last couple years, and Lahm is also a very good player, but on his day Fabio is just sucha good all around player.
He is a:
1) Excellent all around defender.
2) He's really good at getting out of jams and passing/dribbling his way out of tight spaces.
3) He's an excellent passer, he can keep it on the deck, and also lobs up a nice soft long ball.
4) He's always positionally/tactically sound. He's not a overlapping full-back, but he gets into danger areas nonetheless, almost never lets an attacker in behind him on the counter.
5) He takes good free-kicks and corners.
6) He scores goals.
That's a lot of good attributes for a fullback to have. The only big negative he has is that he's always getting crocked. He hasn't had any big injuries this year and his contribution to the side as been really good.
The one worry i have is that he may have earned himself a call up to the Brazilian side. Great for him personally, but the last thing we need is him flying across the Atlantic to play emotionally charged games on hard, dry, pitches.
Hopefully Dunga doesn't rate him.