Disadvantages
xD cards have a small maximum capacity relative to other memory card formats. First-generation xD cards have a maximum capacity of only 512 MiB; while Type M expands the theoretical maximum capacity to 8 GB, but as of January 2009[update] there are no cards available with capacity greater than 2 GiB.
xD cards have not kept up with the speed of other cards, notably Compact Flash and SD. The fastest xD card is less than 10% of the speed of current (2009) Compact Flash cards.
Although physically smaller than Secure Digital and Memory Stick cards, xD cards are larger than these competitors' reduced-size variants (microSD, and Memory Stick Micro).
xD cards are generally more expensive than other memory card types. As of May 2009[update], 2 GiB xD cards cost approximately 3 times the price of same-capacity SD cards.
xD cards are less widely supported by camera, card reader, and accessory manufacturers than other formats.[7]
The xD card format is proprietary to Fujifilm and Olympus, just as the Memory Stick format is to Sony. This means that no public documentation or implementation is available (see below for reverse-engineering results). By comparison, the CompactFlash format is described by completely open and free specifications, and a partial specification for the SD format is freely available
http://en.wikipedia.org/wiki/XD-Picture_Card