The "problem" I see with the Sony is the mount. Forget about using inexpensive Nikon AIS glass... and Alpha lenses is hard to come by here in Brazil, at least at reasonable prices anyways.
Andrew, what do you know about the GH3? Any info on that?
Sure Nikon AIS glass is good value, but you know what - I don't have any. Prefer Contax Zeiss. Sadly those will have to be converted to work on the Alpha mount, rather than adapted.
Yes the mount will be an issue for people heavily invested in non-Sony glass because they can't adapt it.
Maybe Sony have something up their sleeve with the A99 to allow that. So far they have been very supportive of adapting lenses on NEX cameras, even showcasing third party adapter rings in the official Sony Centre here in Berlin and selling them alongside the NEX lenses.
For those with smaller collection of lenses, well the solution is to do a bit of eBaying. Here's what I do if the A99 is the hit I think it will be for video. I'll sell my Samyang EOS mount stuff and replace it with Samyang's Alpha mount versions for same price, possibly the Cine editions that were announced today (14, 24, 35). Another lens I use on full frame is Tokina 11-16mm F2.8 at the 16mm end and that is available for same price as EOS mount version in Alpha mount too. Next up I will likely sell my 85mm Contax Zeiss and upgrade to the newer ZA Zeiss version, though of course it will cost £300 more. For those on budget the Samyang 85mm F1.4 is great value for money and in Sony mount too. Then we come to the Alpha glass, there might be some nice choices there (they have a telephoto lens optimised especially for awesome looking bokeh for example that I thought about using on my existing cameras) but really unless you want AF and some zooms you can save money and stick to non Sony stuff.
As for ultra affordable, what about Minolta primes on eBay?
See, there are options and it isn't the end of the world because of the Alpha mount unless you have tons of L stuff that you can't afford to swap out for the Alpha equivalent. I do agree that the biggest obstacle to Sony's success in the pro market for photography is indeed that people are locked into vast investments in Canon and Nikon glass. If I were Sony I'd make the SLT assembly and Alpha mount detachable from a new mirrorless full frame mount. Essentially imagine the NEX SLT adapter as part of the camera, and it comes off when you need to put on a Canon or Nikon mount instead.