After a short periodn where the amazing attacking machinery of the Catalonians seemed to be weakening, they have apparently returned with force to pose as serious candidates for this years trophy. However, Bayern Munich is never to be underestimated: although not doing overly well in the Bundesliga, they seem committed to showing their strength in Europe.
Surely a difficult match, but I believe Barcelona will prevail.
This is becoming an almost classic encounter, and will be a repeat of last season's semifinal, where Chelsea prevailed after John Arne-Riise's own goal in the first match. In the Premier League Chelsea is behind Liverpool, and has not looked as awesome this season as last, although the arrival of Guus Hiddink as coach may have given them new momentum.
Liverpool on the other hand increasingly looks as the team to defeat after their pounding of Real Madrid and Manchester United in the CL and Premier League respectively. I also think that is why Liverpool will prevail.
This is a repeat of the 2006 Champions League semifinal, which was a first for Villarreal, but where Arsenal prevailed and made it to their first ever Champions League final (where they eventually lost to FC Barcelona). Arsenal is pretty much out of the fight for the English league title, but has a young team that are wanting to show what they can do in Europe. However, their striking force seems to be very poor, and I do believe that Villarreal, although not a strong team themselves (and with awful tendencies to underestimate their opponents) will win.
Manchester United is looking awesome this season (in spite of their recent 1-4 loss at home to Liverpool in the Premier League) and in my point of view are still the favourites to lift the trophy in Rome. Against a confident and always-underestimated FC Porto they will nevertheless face difficulties. FC Porto is still a very strong team and they have managed to upset the Reds before: in the 2003-2004 Champions League season, when FC Porto ultimately won the title, the Portuguese champions eliminated Manchester United in the quarterfinals.
Still, I think Manchester United will prevail this time: the team this season is on a completely different league!