I hate to spoil anything for someone who hasn't seen the Avengers movie yet, but if you haven't, please read no further!
All long-time Avengers fans must have been thrilled to see that Thanos was the mystery villain behind Loki's invasion of Earth and attempt to snatch the Cosmic Cube. I had guessed at his identity early on but was surprised to see they actually animated his face and trademark ruffled chin in the post-script. There is an article over an SlashFilm where Kevin Feige and Joss Whedon talk about how they arrived at using Thanos.
Like most of us, Whedon was a giant-size geek who was into Jim Starlin's early Marvel work. Everyone who read both Captain Marvel and Warlock had to buy Avengers Annual #7 where both heroes united with the Avengers to stop Thanos from destroying the universe. I still own that issue along with the conclusion in Marvel Two-In-One Annual #2.
Seeing Thanos on the big screen was really cool, because with Whedon we have a film-maker who is basically a geek like all of us. He grew up reading comics in the 70s and this helped form his tastes as a writer.
At the same time, it's a bittersweet feeling regarding Jim Starlin, who probably won't receive any remuneration for Thanos or any of his Marvel characters, since they were created work-for-hire. Some of this is discussed in Starlin's recent interview with Geoff Boucher on Hero Complex. While it is true that Marvel doesn't legally have to do anything, you would think at the least they could invite Starlin to a premiere. The classiest move ever was by Paul Levitz after Batman Begins arrived in theaters--he gave a bonus to Denny O'Neil, Neal Adams and others who had created the characters used in the film. Marvel and Disney don't have to do it, but wouldn't it be great if they did?
Check out Jim Starlin's profile on Facebook, where many of these Thanos commissions originally appeared. Nuff Said!