Both are finally out, so if you have lots of Canon glass, you have a low weight APS-sized alternative at least until the cool small camera come out that are mirrorless. Both are 18MP and have the new autofocus systems of the 7D with the new Canon 60D
Also, a bunch of cool new lenses are out. The most notable is the 8-15MM F/4L (that’s right 8MM) fish eye that is pretty cool. Also if you take lots of sports then the new 400M F/2.8 IS USM is the one to look at if you can afford it. Super fast and high zoom. In APS, that’s a 600MM equivalent!
And of course the big news is that Sony A55 continues to move really rapidly ahead introducing a translucent mirror camera. This means you get continuous autofocus in movie mode. Really too bad I have to much Canon glass! This is a big brother to the NEX-5 and seems easier to use.
Overall, if you want a lighter camera, then the main word is a wait a bit, there are so many choices just settling down. Sony has got some great technology in the NEX-5 but it is too hard to use. Nikon is rumored to be releasing a mirrorless design. And if you just want a lighter compatible Canon then the 550D looks like the ticket.