I've been keeping an eye on the odds for the US Open. They'd been holding steady though the last two tournaments but there was a bit of activity in the last week even though no top players were playing. I'd guess that's just because people are only starting to bet now.
Federer's odds have shortened a bit while both Murray and Nadal's have lengthened.
Interestingly, Federer's odds are now the same as Laver's before Wimbledon in 1969 and yes I do think that's significant.