Well, Maxy, that's due to the game they played against Barca beforehand a few years back. Chelsea are one of the few sides in European games to go and play a blinder against Barca and likely would have beaten them were it not for some attrocious refereeing.
There's also the whole rolling about/cheating the referee thing which they still do. I do love watching Barca play, and would say I'm a "fan", but you can't be blind to your team's failings. Alves, Busquets, Pedro and Sanchez are especially bad at this sort of thing.
Overall, I'd say it will be a win for Barca (no suprise they are favourites for the cup), but if Chelsea play well they should give them a good game given how frail Barcelona's defence can be.
I remember the game very well... However I totally agree with Zzeezzy, Chelsea is no where near as good as the 2009 team. Seeing how Benfica passed rings around chelsea at times, I can't imagine what barca will do to them. Especially with Messi on the form he's in atm: he'll be hungry for 70+ goals this season.