I agree with TurboTiger - if you can afford more RAM, do (that goes with any computer, regardless of OS, as you know) and similarly, grabbing more storage - 256 rather than 128.
That said, I moved to Mac (and the 4 RAM / 128GB SSD mid-2011 Air) from PCs when Microsoft went to Win8 - and, after the learning curve dealt with, I have been perfectly happy with it. Storage was a concern for me when I was first looking at them, but now I have a whack of documents, hundreds of photos, ditto music and 25 videos onboard - and still have 35GB free. Backups and stuff I use less regularly I have on a partitioned portable external drive.
Despite the 4 RAM, it doesn't struggle all that often, but then, I don't try and do any heavy-duty processor-heavy computing, like video editing. As with TurboTiger, it does the job for me!