Georges St. Pierre vs Anderson Silva in a catch weight bout at 180 pounds would be the biggest fight in UFC history for many reasons. There has been big debate for many years as to who the world's best pound-for-pound MMA fighter is, and I believe we may get to see that put to the test in 2011.
GSP and Silva both have a huge allegiance of fans laying claim to the pound-for-pound best fighter title. They are without a doubt the most well-rounded MMA fighters at the present time, and a catch weight bout between the two would settle once and for all who the world's best mixed martial artist is.
Obviously these guys are too small to fight Brock Lesnar, Shane Carwin, or Fedor Emelianko; however I doubt many people would have a problem crowning this fight's winner as the pound-for-pound champ.

Time is Running out
Anderson Silva has stated publicly that he plans to retire when he turns 35, and guess what, he just did on April 14. However, his upcoming fight with Demian Meia dispells that claim, and knowing Dana White, anything could be worked out. My bet is, we will see this fight happen early 2011 Win, lose, or draw, this will be Silva's final fight.
Would he take the fight? Sure he would. A win over GSP could cement his legacy as the greatest middleweight in UFC history. Would GSP take the fight? Sure, and for the same reason. Both fighters have taken catch weight bouts before. Both fighters have a huge repect for each other and the sport.

Collision Course
GSP has been going through opponents in the UFC the last few years the same way Silva has: with ease! His last loss was in April 2007 against Matt Serra. He later avenged the loss against Serra, as well as his loss to Matt Hughes in devastating fashion. His 20-2 record sits atop the UFC, and as welterweight champ, he looks pretty unstoppable.
Everyone who is sent to Challenge GSP really has no answers on how to complete the task, and simply get the weak spots in their game ripped apart. He's cruised through Thiago Alves, Karo Parisyan, BJ Penn, and Dan Hardy in similar fashion to the way Silva has cruised through Forrest Griffin, Dan Henderson, and James Irvin.
Anderson Silva sits at 25-4, and he hasn't lost since January of 2006 against Yushin Okami, but that was a disqualification due to an illegal kick. The last time he was clearly beaten was December 31, 2004 to Ryo Chonan. He holds the most consecutive wins in the UFC, and can add to that streak as it is still current.

What lies ahead?
Well for GSP, it will be the winner of the Paul Daley/Josh Koshchek fight. In my opinion, his next match will be another take-down clinic, and for the blood thirsty fans that attend UFC fights, uneventful.
Daley has big punching power, but I have a really hard time seeing any thing different than GSP vs Hardy part two. Their style is practically the same, in fact, they are friends and sparring partners. Big hype? Sell a lot of pay-per-views? Probably not.
If Koscheck wins, and I clearly see this happening against Daley, we will have Koscheck vs St.Pierre again, just a repeat of UFC 74. Big Hype? A little, but big pay-per-view sale? no.
As for Silva, time is of the essence. His fight with Meia, I think 95 percent of the fans voted the same way as to how this one will end up: Silva with his hand raised. Big sales, big hype? No.
What will be interesting though after the Meia fight is the reemergence of Vitor Belfort. But as always with Belfort, which fighter will show up to the fight? In prime form, this could be very interesting, as Belfort possesses the power and speed to knock Silva out at 205 or 185 pounds.
Every MMA fan has a little bit of " Blood thirsty mentality " in them. And that really just hasn't been getting delivered in these slow, controlled, dominant performances. I won't even address the Silva vs. Griffin fight, which I have serious hang ups to its hollow finish full of questions (but that's another story).

Likely play out scenario:
GSP cruises through his next two fights looking in full control, and totally focused. So does Anderson Silva. Then what happens? Does the UFC just keep trying to hype fights that people really cant get excited about. No offense, but Silva vs. Meia is about as exciting as watching water boil.

Feeding the Haters:
With success comes jealousy, and the man with the upper hand has to face this opponent daily. GSP and Silva face criticism all the time. This may fuel this fight as much as people who like them both (aka the people who just wanna see a guy get beat because they don't like him).
My prediction is that by the middle of 2011, this fight will take place. I believe the will meet at 180 pounds and set up the super fight. I agree with the GSP fans, and the Silva fans when they say their guy is the best. They are both incredible athletes and as well rounded as you can possibly be. And we will find out who is the best of the best.
If Dana White lets Silva retire without setting this fight up, it would be his biggest mistake since becoming UFC president. Silva vs Meia proves just as little as GSP vs Koscheck Two. Gaining or losing 20 pounds to make weight is nothing for a professional fighter. I think this collision course is three years in the making. It would be the biggest headline and most anticipated fight in UFC history, and it will generate huge revenue.