I, too, have been using '08 for a couple weeks now. I had problems with the new source dialogue originally when I tried to copy/paste a source title as I had done before in version 16. The program would shut down immediately.

I have started using Edit/Manage Sources first and either editing a previous source or creating a new one (whichever I happen to be doing at the time). Then when I go to use the source in the program, I click the new source button and type the first couple digits/letters of the source to see it pop up in the box (or close to it). Then I use the drag down arrow to get to the source itself.
So far it has worked perfectly this way.

Hope this helps.