My card is a 2 GB and used to serve as a regular mobile phone storage. When writing for example music on that card it took a lot of time. This goes to show Micro-SD cards are, eh, slow.
After downloading RISC OS I wrote the image and was ready to boot Raspberry Pi - with no success. I only got 640*480 RISC OS boot screen saying there's nothing (or enough) on the card. Now what? I downloaded an update which I renamed as RISCOS.IMG. After that I replaced the old file with the newer one on the card. That helped! I got an extra harddisk for Raspberry Pi! RISC OS is so lightning fast it doesn't matter if Micro-SD -card is a bit slow.
Micro-SD -card bottom right and the adapter above the card.