I upgraded several days ago and posted a question about the accelerators here:
I am finding it to be a lot slower than IE 7. I think it is due to all the new filters they've created in an effort to make the browser more secure.
IE 8 also has conflicts with several programs on my PC, Skype being one of them. It required deletion of Skype's quick launch icon in the task bar and reinstalling Skype did not remedy the situation. It is still useable, but I have to go to the start menu to launch it now.
I don't really understand the purpose for the Suggested Sites or Web Slice Gallery yet and am not using them. To me, they seem to be nothing but usage tracking devices designed to overcome the cookie blocking most users invoke.
Once you get used to using them, you'll like the accelerators, especially for sites like Digg, Facebook, Stumble It, etc.
There are accelerators for many types of sites. You can view a list of them here:
And further reviews and descriptions of the new IE 8 features here:
The new features do not make up for the slowness of it. If I can't figure out how to overcome the slowness, I'll probably be reverting back to IE 7 soon.