The Photoshop CS5 12.0.1 update increased the amount of RAM that Content Aware Fill can access. It is now limited (when running Photoshop in 64-bit mode) only to the amount of RAM in your computer. The error "An unexpected and unrecoverable problem has occurred ..." is fixed in this update. Other memory errors, especially if you are running Photoshop CS5 in 64-bit mode, are also solved with this update.
Content Aware Fill requires large blocks of contiguous memory (RAM). On 32-bit computers, where you are limited in the amount of RAM Photoshop can access to ~2-3 GB, normal use fragments RAM into smaller blocks. Refreshing the RAM sets it back into one large block. If you don't crash when you run Content Aware Fill, and your RAM is limited, refreshing your RAM can solve memory errors and speed issues. Refresh your RAM again as you use Photoshop.
The amount of RAM Content Aware Fill uses depends on the size of the selection area you create for the fill. To use less RAM, draw your selection area closer to the object you want to fill. For example, if you want to remove an electrical line that runs through your image, draw your selection close to the line.
When you use Content Aware Fill to create the missing pieces around the edge of a panorama, choose each section of the panorama separately. Run Content Aware Fill on that individual section. Selecting the entire image to fill all the missing edge pieces takes a considerable amount of RAM. Filling a large image can fail, especially when you run Photoshop in 32-bit mode, or your computer doesn't have enough RAM.