I'd say this year is going to be very hard to call as there are so many factors that could change the equation entirely but here is my best guess.
I think the PS3 is going to be flat or slightly up. I don't think we are going to get another price cut this year. I really think we are getting beyond the point where a single software release can have a huge impact on console sales but still I'm hesitant to discount the effect of GT5. At the moment I don't see the wand having a big influence this year unless it comes much earlier than expected and is very well supported. We are not going to see crazy weeks that we saw post slim release but sales are going to be more consistent than last year and with GT5 and generally strong software i think it will end at 13-13.5 million.
I feel the 360's fortunes largely rest on Natal, when it releases, software support and whether follow up press is as positive as the initial press. If Natal hits a positive note then I can see it having some impact on hardware sales especially towards the holiday season where irrespective of software support it could become one of the new, cool gadgets to have at Christmas. 10.5-11 million.
Wii could very well go up, down or stay the same this year. Nintendo has professed that they don't want to lose momentum again so I think they will be more proactice this year in ensuring there aren't major software gaps at least on the first party front. They have Mario Galaxy 2, Metroid Other M, Zelda Wii all slated to release this year and less certainly Wii Vitality and Retro's game. With carefully timed releases this should keep the core gamer happy for most of the year so for me the big question lies with Wii Vitality. For the Wii to go up i think it would require at least one of two things; greater core adoption for the growing list of must have 1st party titles or Wii Vitality to have appeal on the scale of Wii Fit. Sales of the Wii will eventually have to drop to levels of a mortal console but then again we've been saying that about the DS for several years. I'm going to work on the assumption that Nintendo is going to get 'it' right this year, buck the YOY drop and end at about 22.3-22.8 million.
I am kind of going for a best case scenario for each of the three consoles but with the economic situation currently looking more promising than a year ago I don't think it's impossible.