You can use any manufacturer's card. Lexar, Fuji, Edge, Kodak all make this type of memory in addition to Olympus.
The SP-350 camera can utilize the Olympus branded xD cards for automated panorama stitching in the camera. Most photo programs offer something similar. The Olympus Master software comes in two levels. A basic level is free, the advanced level must be purchased. I already sprung for PhotoShop CS2 so I am not bothering with the Olympus software.
There are two speeds of cards currently available. The original is an xDM and a newer, faster model is the xDH. Write speed is the chief difference between them. There is a noticable decrease in time when taking RAW photos. The xDH takes 7-9 seconds between shots, the xDM does the same task in 12-15 seconds.
This can take slightly longer if you save a JPEG image along with the RAW image. However, if you want to quickly review your photo whilst shooting to the RAW format, saving a HQ JPEG will make this a lot easier. Otherwise you will get to wait just as long for the camera to read the image as it took to save it.
If I'm using a strobe I usually shoot SHQ JPEG's. I don't like the long wait necessary to write RAW image data to memory. If I was shooting a wreck or without flash I might use RAW. It gives one greater latitude for processing.