I posted a link for you in your mobo thread: PCIe 2.0 dictates twice the throughput of 1.1. 2.0 is forwards and backwards compatible: meaning you can run 1.0/1.1 devices in a 2.0 slot, and also run 2.0 compliant devices in a 1.0/1.1 slot.
Now - As far as "real" performance increase? That's going to be difficult to pinpoint. Why?? Because the existing standard isn't close to it's limits. If you'll allow me to make up some numbers: Think of it as doubling the speed limit on the highway from 70 to 140. If no cars exist which are powerful enough to go faster than 50 miles an hour, and there are enough lanes to fit the traffic, does it matter???? This is like the situation now. Even multiple devices aren't capable of running faster than current limitations. So increasing the capacity of the pipe isn't going to bring much 'real world' benefit. At least the way things stand at the moment.
And
Yes, I look forward to the day when I can spend some of my hard earned on a "100+ MPH" Graphics card....