Here is my experience with 2008.
First, don't run it on Vista, because Vista sucks. Not a VS 2008 issue, except that Vista was also created by Microsoft and someone from the VS 2008 team should tell the Vista team they suck and quit screwing developers that are using Visual Studio products.
Second, the 3 year release cycle that MS is trying to do is crap. Fix the current products and make them usable, instead of trying to meet a dumb 3 year release cycle that screws every developer and every corporation in the world because of ramp up and migration costs, etc. VS 2005 had 1 service pack, you had to live with the rest of the buggy stuff.
Third, I do like the integrated Designer, although it is buggy and you can't rely on it, it does help with CSS better. (which is the result of Expressions Web product). One thing that upsets me about doing any sort of design with VS 2008 is not necessary the product, but the browser. IE 7.0 is slow as heck compared to firefox, so when I do have to run the app because I'm doing design and the designer doesn't work, it is SLOW. Also, I have to double check my work with firefox anyway because IE doesn't follow CSS standards which is another problem I have with MS.
Finally, I think VS 2008 is just as buggy as VS 2005, (some things were not even fixed from 2005), so as a result, you might as well make the jump to 2008 to get the javascript debugger and the better CSS support. And if you have Vista, get rid of it because it sucks when you try to use any Visual Studio Development tool.
It is a sad day when you have to make a decision on what is the least worst product to use. Unfortunately Microsoft is putting us into this situation with Vista and Internet Explorer 7.0. Those products are far from meeting the old Microsoft standards and they will eventually tick off enough people to shift browsers.