*** This thread should be deleted. I assumed the last shipped developer preview was using 4.1 for it's Docs app while it wasn't the case and the docs was still running on 4.0.7. ***
I already posted about Docs poor performance with 4.0 in IE 8. I was hoping to see an improvement in 4.1, but it's not the case. Booting the app fresh still takes ~19 sec of JS crunching while switching between two class tabs takes ~3 sec.
You can find attached to this post the results of the profiling for both operations. The .zip contains two .csv files.