To those thinking that Sony is not a big player yet...
True, Sony is not a big player... yet. I predict that in 2 years, Sony is going to be much more important. If Nikon does not follow with more serious video feature, they might become a bit like Leica... Giving much more room for Sony to compete against Canon in the consumer market. I hope Nikon stays in the competition and we're going to see that in the next few months. Even if Nikon stays very strong, I believe Sony is getting stronger and stronger.
They are the only non-Canon or Nikon company to offer the Full frame sensor in a DSLR.
Sony also offers a nice range of lenses including 16-35 ƒ/2.8 and 70-200 ƒ/2.8 both for FX format. They pretty much have all the most important lenses by now and I guess they are working on more macro, T&S, exotic telephotos, wide angles, etc. They already started it will only continue.
They are also about to offer video in their DSLR, considering Sony's experience with video features, it will probably be as good as Canon's video feature in the 5D2.
They have that new kind of sensor coming, if it's really as good as they say in a DSLR, many low light photographer will be tempted, including me.
I believe that Sony, as a bigger company, as the power to compete with Canon much more aggressively than Nikon. Even if the later is very strong due to their fanboys. However, if Sony finds a way to offer much more for the same $, they are going to steal customers to both Canon and Nikon, even in the professional market. I wouldn't be surprised to see that Nikon turns into Leica in the next 5 years, although, I hope they stay strong.