From a friend: "Installed Ubuntu 9.04 on Asus Eee PC. Recently discovered that, when an SD card is in the reader, the boot freezes. Once I remove the card though, the whole thing restarts and everything works normally. Should I be concerned?"
As far as I can determine, it has something to do with driver incompatibilities. The solution? Until someone takes the time to create something definite, I suggest you just keep your card out of the slot when you boot up