+1 on the 28 1.8 - love it on crop and FF.
The funny thing is, I find that I get pushed into a different mode of sorts with the 40.
I feel the need to get in closer, and push different angles. This is the case with both a 5D2 and 7D.
Lots of fun. Similar in this regards to the 28 1.8 on the 7D.
With the 50 1.4 its a bit of a more classical feel; and I don't get the urge to perform acrobatics while shooting.
Having both, I can't say that I would give up one over the other. They each give a difference experience. I will admit though, I still use the 50 more. Since adding the 40, I would say its approx 4:1 shots taken (mostly low light).