I had the same issue and just did a search for Minecraft 1.5.2 Mac and downloaded the old version. Now everything works again, and I will just wait until they have fixed this issue before updating again.
You can do that or what i did might be easier, if you havent deleted your old launcher use that and do fource update and you will have 1.5.2 again. I just orderd snow lepord from mac this morning so ill go withought horses until it comes.
Ugh. I cannot afford snow leopard but apparently we need it to play now. What's even worse is that since this is a major issue, you think that it would have been in the 1.6.2 change-log, but it was not. Therefore, unless something changes between today and july 8th when the update comes out, mojang is forcing us to upgrade or stop playing minecraft altogether. Even if I could afford snow leopard, I don't play on my own computer and the person who owns the one i do play on won't let me get snow leopard. If mojang is really going down this path, then they are going to lose a lot of customers.