I don't know if this was posted here before, but over at the anandtech forum the tech editor shared a few days ago some of his experience with Barcelona. To summarize:
1. Barcelona will show its power only above 2.4GHz. So don't expect fireworks on launch date.
2. Over the last few months each stepping showed a marked improvement over the prior one. Current stepping is B02, which will make some people happy with benchmark results, and some people not - depending on the particular application.
3. All past benchmarks and related hints are not reliable, since engineering samples had various sub-systems switched on or off - depending on the particular sample on hand.
4. The next stepping to come, B03, supposes to show what Barcelona is capable of, but this will not be evident on Sep 10th.