I think the tie depends largely on whether Gallas and Makalele are fit. Gallas in particular is crucial because without him, Chelsea have to choose 2 from Geremi, Del Horno, Johnson, and Ferreira for the fullback slots. It goes without saying that Johnson would be eaten for lunch by either Ronaldinho or Messi, so he's out. Likewise Geremi probably isn't up for it. So that leaves Ferreira (who is still probably traumatized by what Ronaldinho did to him at Stamford bridge last season) and Del Horno. That creates two favorable matchups for Barca - or more accurately, it helps negate the fact that Belleti and Gio are most likely going to be owned on the other end. Without Makelele and the suspended Essien, Chelsea are forced to play Gudjohnson/Cole, Lampard, Maniche as their midfield three. That may mean Lampard will have to actually defend sometimes on Wednesday, especially since Maniche isn't looking great right now, which will lessen his attacking threat. I'd say in that case the midfields are pretty even, maybe a slight advantage to Barca. With Makalele, the advantage goes back to Chelsea. I think Barca's key man for the match will be Van Bommel. Barca's ability to stick to the tactical gameplan and not get too excited (leaving holes at the back) rests largely with him.