I bought the Colcasac Zagora a few weeks ago. The first one they sent me seemed a bit big, which turned out to be the wrong one. It was one for a 13" MBP, not the MBA. The second one they sent did seem smaller, but the fit was not 100% on the 2010 13" MBA. It was just a tad bit too tight, and the sleeve is crooked. So I asked if they could check their inventory and make sure the next one is right. When I received the third one, it was also not right even though they tested it.
Customer service has been friendly, and great. However, I do not believe they had the right measurements for the 2010 13" MBA.
I just emailed Colcasac again, so I hope they can correct this. At this point, I could not recommend the MBA one. However, the MBP 13" is great! =)