Just in case you haven't been following what people have been saying about the dual spec system lately, Slashhug has a terrific post up covering all of the concerns and thoughts about the new system and how it will affect groups and raids. It's long, but he covers all of the bases, from how hybrids with two specs will affect which players get chosen for groups, to loot and how that will work (the same -- main specs first, offspecs if needed), and even soloing and why dual specs will be a blessing for classes who are normally built more for group play.
There's not a lot of new complaints or answers in here -- lots of it has already been discussed on the forums and in our own posts. But Slashhug does a great job of wrapping it all up into one big tasty dual spec sandwich, so you can catch up on all the thinking about dual specs so far. The bottom line, in terms of player reaction, is that dual specs will allow you to do more with your class than you can with just one spec. If you want to heal, you can still heal, or if you're built for tanking, you can still do that. But in groups where things don't quite fit (you've got a few tanks and your DPS is a little low, or your Priest could use a little extra help healing for this boss fight), dual specs will let you make the necessary tweaks right then and there, and excel that much more.
Patch 3.1 brings us Ulduar, dual specs, significant changes to all the classes, and more! We've got you covered from top to bottom with our Guide to Patch 3.1.