What is normal?
Never seen so much crap talked about 2GB v 4GB. I have just bought the basic 11" model, and for what I use it for, along with probably 90% of the members on here, it could hardly work any faster.
Granted I am not using Autocad 2011 or intensive Photoshop work, but you are talking about returning it for a 4GB model, and it sounds as if you are going to do that purely on reading some of the posts on here as opposed to having a problem with 2GB.
I read continual posts that 4 will make so much difference compared to 2, but IT WILL NOT in normal usage. Neither will 1.6 compared to 1.4, but obviously a 128GB SSD as opposed to 64 will do if you need the extra storage.
Work out what you are going to use it for, then start working out if you need upgrades which will cost you hundreds of dollars.
tut
I don't want to start a flame war, just note one thing: what's normal usage? It varies from person to person.
2GB are enough to you and I believe that. To me, 4GB makes a lot of difference. It all depends on your daily (aka "normal") usage.
Just as a reference, I'm a software developer. I write web sites and backends in Ruby and use Safari, Chrome, Vim/TextMate, MySQL (and other databases, sometimes concurrently) and a web server for local development. Add to this all the "trival" stuff I use (like Adium, Sparrow for GMail, Twitter for Mac, Dropbox, Droplr, Jumpcut, Caffeine, iTunes) and OS services like Spotlight indexing, and 4GB is a nice jump. I had a MacBook with 2GB until some time ago, it wasn't unusable of course, but it swapped all the time.
Just my 2 cents.
Update: here's my system memory stats:
http://d.pr/17SL