I've been following the Raspberry saga with interest. I don't think any of them are out in the general world yet as the first batch had to be reworked due to Ethernet jacks that lacked isolation transformers. The information I saw on the PIC Microcontroller list said they might be ready by June or July. If the ARM version of speakup works like the i86 one does, there is no reason why it shouldn't work on a Raspberry Pie. The question may be how well will speakup work when compeeting with other applications on a Raspbery Pie. I have seen speakup work pretty well on a box with only 64 megs of RAM but the speech got pretty hoarse if the system was trying to log or do anything else while it was talking. It worked, but it wasn't pretty.
