Thanks to a lot of conflicts and two crazy jobs in the past year I am behind on my book reviews. That makes writing them a bit tougher as I have to root around in my entirely inadequate memory for what I thought of these things months ago when I finished them. I'll do my best...
Vacuum Diagrams is a collection of science fiction short stories that collect and intertwine the author's larger works in a (relatively) cohesive whole. Baxter actually pulls this off better than many - Asimov and Heinlein come to mind as examples of those who should never have tried such a thing - probably because he actually did have a relatively cohesive world view as he wrote his various works.
Nevertheless, while I found these stories acceptable, they really didn't stick with me. There's something about huge, sweeping tales - these cover the entire history of our universe, and introduce a second, if that makes any sense out of context - that makes me want more than just short stories to get them to stick.
If you've read other things by Baxter and enjoyed them then this may be your thing. You can see the overall view of the universe(s) he imagines here. For me, though, these were simply OK stories without enough glue to make them work overall.