Okay, let's review. Hard drive manufacturers have always used decimal gigabytes (GB) to measure sizes. Windows and Mac OS prior to 10.5 used binary gigabytes (GiB), resulting in a size discrepancy. 10.6 now uses decimal gigabytes, and is consistent with hard drive manufacturer units. So, my 250 GB hard drive is reported as having 250 GB of total capacity, and 250,000,000,000 bytes (plus some change). Now - the new MBA 11" 128 GB is advertised as having an 128 GB SSD. However, Mac OS X 10.6 reports it as having a total capacity of 121.3 GB (121,300,000,000 bytes) in "About This Mac". What's up with that? If 128 GB actually means GB, then that translates to 119.2 GiB. Clearly not the problem (and we know that 10.6 does not use GiB anyway). If 128 GB actually means GiB, then that translates to 137.4 GB. Clearly not the problem either. Clearly it is not formatting overhead either, because my 250 GB conventional hard drive is reported as a total capacity of 250 GB, meaning "About This Mac" does not perform any correction for formatting overhead when reporting the total capacity (not that I would expect it to). What's up here?