Nothing to do with Vibrams, but there have been some really good reviews for Toe Stretchers from JD Harris: http://www.jdharris.co.uk/toe-stretchers but they're cheaper if you buy them from Amazon: http://www.amazon.co.uk/J-Harris-Original-Stretchers-Spacers/dp/B0045D47V6/ref=sr_1_1?ie=UTF8&qid=1332282673&sr=8-1
I bought some last week but not used them enough to be able to comment.