I am also curious to know when to expect movement on the alternate list. I have been accepted to a school on the east coast, but I would prefer to stay in Oregon. I have searched OHSU blogs like this one from previous years in order to provide an idea for what we might expect this year.
In 2005, the first mention of movement on the alternate list was on May 26th, and the person leaving the post had been accepted from their #4 position.
In 2007, the first mention of movement on the alternate list was on June 4th, and they had accepted through #24 at that point.
That was all I could find regarding the original movement on the alternate list in previous years. While this information may not be reliable for this year, OHSU does seem to be consistent in having May 15th as their final decision day, and so, it would not be all that unreasonable to assume that they start choosing people from the alternate list around the same time as well.
Additionally, I have been able to find the amount of movement that has occurred in previous years on OHSU's alternate list, some of which has already been posted earlier in this blog:
In 2003: #90's, 2004: #64, 2005: not sure, 2006: #98, 2007: #77, 2008: #57, 2009: #?
Hope this information is helpful. Good luck to everyone!