For those who are enthusiasts of team tactics, here are the key points to watch for:
* Pressing: United came out strong in the 2009 final, and almost scored early when Park came close to finishing off a Ronaldo free kick. That kind of pressure was hard to sustain, and after conceding in the 10th minute, United were chasing the rest of the match.
There are different ways to press, and whether it be by stepping up higher on the pitch (which might expose Vidic and Ferdinand at the back) or blocking the midfield third to lead to United's counter-attack, how United are able to press Barca will be a key.
Keeping an eye on Xavi and Iniesta will be the key to United's success - both players have the ability to unbalance an opponent by disrupting their shape by their movement off the ball, or their tremendous decision-making in possession by knowing when to keep the ball and when to stretch the opposing defense.
Along with keeping Xavi, Iniesta, Busquets and Co. under pressure in midfield, the backline has to be able to keep Messi and Villa with their backs to the goal and under extreme pressure as well. Laying off Barcelona allows their key attacking players get a rhythm and is hard to disrupt - Manchester United can't give them too much respect, and allow them to develop a flow early on.
Barca is probably the best pressing team in the world, and due to their ability to keep the ball for long stretches, is probably the most underrated part of their game - they win the ball back as fast they lose it, which puts the opposing midfield under tremendous pressure. Whether it by making United's midfield chase or by putting them under immediate pressure after losing the ball, Barca's midfield pressure will be a key for their success.
Manchester United will need to be able to keep the ball better than they had in 2009, and make sure they are able to punish Barca by getting behind them when they win the ball. Michael Carrick and Ryan Giggs will be key to United's ability to retain possesion and to initiate counter-attacks. Darren Fletcher and Anderson may also play a strong role in that if United opt to play with 3 in midfield.
* The counter-attack: Manchester United may be the best counter-attacking team in the world, and can get in behind on the break in so many different ways. Shutting down the likes of Javier Hernandez, Wayne Rooney, Antonio Valencia, Nani and Ryan Giggs when United win possession will be critical for Barcelona to find success.
Watch for the cover that Barca provides on their left, as either Eric Abidal or Carles Puyol will have the task of shutting down Valencia. The Ecuadorian is as pacy an attacking player as there is, and with either the rusty Abidal or slower Puyol matched up with Valencia, this could be a key that United will try to exploit on the break.
* How will Manchester United line-up against Barcelona?: Ferguson has been partial to a 4-4-2 in the English Premier League, and some variation of a 4-5-1 in Europe. Looking at the success that teams that have defeated Barcelona in this past season (and they have only been defeated 4 times in all competitions), it has been in an alignment that looked like a 4-2-3-1. Playing with two holding midfielders allowed those teams to put more pressure on the Barca midfield by matching up in there, and congesting that midfield 1/3.
Based on convention and historical reference point, Sir Alex Fergson really has two options as they select their team for today- stay in their 4-4-2 that has had a lot of success the past two months, and ask Wayne Rooney to drop in on Busquets when Barcelona has the ball (resembling a 4-4-1-1); play a 4-2-3-1 themselves with Fletcher or Anderson joining Giggs and Carrick. Deploying a 3rd central midfielder could also offer the option of marking Messi with a holding player, much like Mourinho had used with Pepe as Real Madrid defeated Barca in the Copa del Rey.
It would be a hard decision to break up the combination of Rooney and Hernandez, as they have been pretty potent together. With question marks on Barcelona's back line - Puyol might have to push to the left back and Mascherano or Busquets dropping in at center back - the pace of Hernandez and creativity of Rooney underneath him in a free role might be the key to unlocking Barcelona's defense.
My guess is that United will use one of those two alignments (and likely both at different times in the match), with either Rooney dropping in underneath Hernandez, or with Fletcher getting the assignment in midfield and Rooney playing up front on his own. Park and Valencia will probably be selected on the flanks, but if Ferguson does opt to play 4-2-3-1, I could see him making a change at some point to bring Hernandez on and push Roon out on the left. He is most comfortable playing underneath a central striker or drifting out onto the left channel, so I don't know that playing as a lone central striker fits Roon.
The 2011 UEFA Champions League final should prove to be a tremendous match and outstanding tactical chess match.