Google had invited some webmasters and power searchers to test google caffeine, and asked for feedback. The test link is no longer worked, but here has some pictures.
This is for new infrastructure
This is for existing infrastructure
Now we can see that the UI not changed and the search results were fairly similar, but the news moved to the middle.
Just like Google developers said: most users would notice little immediate change. But we surely google caffeine will have significant impact on site owner, since they also said that the changes are“primarily in how we index”.