The Air will work with most iLife apps, including iMovie and GarageBand, just fine. Even though it has a "slower" processor, the way it's designed with solid state storage and an integrated GPU allows it to perform just fine with what most of us use a Mac for. The only reason to have concern would be if you are using "pro" apps such as Final Cut and Logic.
I'm dealing with the same issue, and helping some clients decide which is best for them, so this is something that is fresh in my thought process. It really comes down to whether or not your willing to pay for the sleekness of the Air. The solid state storage also has some benefits, both with performance and sound quality. I'm a big believer that SSDs allow a Mac to sound better for music playback, and most people who have used (listened) to an SSD Mac find it difficult to go back to a standard hard drive. Adding a SSD to a MacBook Pro is not cheap, so in that regard, the Air isn't as expensive. Decisions, decisions, decisions....
I'm dealing with the same issue, and helping some clients decide which is best for them, so this is something that is fresh in my thought process. It really comes down to whether or not your willing to pay for the sleekness of the Air. The solid state storage also has some benefits, both with performance and sound quality. I'm a big believer that SSDs allow a Mac to sound better for music playback, and most people who have used (listened) to an SSD Mac find it difficult to go back to a standard hard drive. Adding a SSD to a MacBook Pro is not cheap, so in that regard, the Air isn't as expensive. Decisions, decisions, decisions....