First, you need to realize that OS X is simply not as efficient at running HD apps or apps without h.264 hardware acceleration. Times are changing and Apple FINALLY just gave low-level access via APIs to developers to use hardware acceleration of h.264. Things will improve, but for now, Windows 7 provides the best performance on MBAs without any problems as you reported.
Running Windows 7 on the exact same MBA, you wouldn't experience one problem whatsoever. I know because I do it all the time. HD apps that have h.264 do just fine in OS X. Anything in a browser in OS X can be problematic, but it's getting better. With the latest version of Flash, it's a start at big improvements in OS X. However, the MBA runs entertainment apps, h.264, and OpenGL much better in Windows 7. The components in the MBA are plenty capable, it's Apple controlling the environment so much as why OS X is worse than Windows 7. So "stability" comes at a price for OS X users. We can see it with Flash, HD apps, h.264, and anything OpenGL related.
Do not buy an HDD MBA. Understand that the drive and drive controller are the ultimate bottleneck in today's computers. Before people should want faster CPUs, more RAM, and etc, they should absolutely ensure they get the best performance drive possible in their computers. You will be waiting and waiting on the 4200rpm HDD all of the time. It will be beachball nightmares a few days in, and you will ultimately suffer for buying an MBA. I would recommend anyone buying an MBA spend $50 more than the HDD version and get the faster 2.13 GHz CPU and 128 GB SSD for $1549 refurbished at Apple.com. Buying the SSD is worth every penny, and it has the same warranty and is in the same condition as new when you buy an MBA. OR, if you wish to save some money from the $1499 price tag, the 1.86 GHz with 128 GB SSD is available for $1349 refurbished.
Whatever you do, do not buy the HDD version, as you will be truly disappointed and waiting on the MBA all the time. If someone must buy new to get the MBA, they absolutely have to come up with $300 more for the SSD version. If you cannot afford it, buy the 13" MBP instead. I wouldn't recommend an HDD MBA to anyone no matter how inexpensive or how much they "save" in money because they will spend their lives waiting on the worthless HDD in the MBA. If you cannot afford the right MBA, don't buy one. You will be much happier with a 13" MBP that is incredibly faster than the HDD MBA.
The MBA is plenty capable. Either run Windows 7 on it or ensure you keep on top of updating Flash and HD playback software to ensure latest versions using APIs to do h.264 hardware acceleration. In addition, make sure you buy the SSD version and go with the cheaper refurbished versions if you have to. Good luck with whatever you buy.
