I got the 4 GB and have not had regrets. I had 8 GB on my old Macbook Pro and always maxed it out. The 4 GB I currently have is always maxed out. From what I can tell, this is kind of just the way Mac OS works.
But to say that it is maxed out does not mean that it is slowed down. I do programming on my MBA and have had no problem. At almost every moment that I am on my MBA I have 9 programs open: iTunes, Calendar, OmniFocus, Microsoft Word, Scrivener, Sente, Devonthink, Outlook, and Chrome. I often also have two-three large (200+ MB PDFs) open along with all of these programs.
Now, none of these are particularly resource heavy such as movie editing or image editing... But I must say, I am more than amazed that I can have all of these open with ZERO slow down.
Do I wish I had bought 8 GB? Yes... But I am only completely satisfied when I max out my technology. However, I bought a "low-end" MBA and the only upgrade was to 256 GB HD. And this has not affected my experience a single bit, except I personally like to have maxed out technology.
To be 100% honest, I can only recommend getting 8 GB if you do movie/image editing or you want maxed out technology. Though I will say, I feel that I could have benefited from a better CPU whenever I code number-crunching programs.