According to the latest post on the Raspberry Pi website, “The Raspberry Pi Foundation will be making a big (and very positive) announcement that just might interest you at 0600h GMT on Wednesday 29 February 2012.”
This is expected to be the first batch of the tiny computer going on sale; Eben Upton posted a status update on Saturday morning saying that they had “been assured this morning that a first batch of boards will ship to us either today or first thing Monday” – adding that “if you don’t own an alarm clock, this weekend might be a good time to do some shopping.”
Do bear in mind, of course, that while the RISC OS port is underway, it is still not complete – there remains work to be done. However, over on the RISC OS Open forum, Theo Markettos suggests that it might be helpful if a few people try to purchase one, either to help with development themselves or to lend to other developers working on RISC OS.