Came in the mail today and I put it on my XTi and took a few test shots and am EXTREMELY please with it for the $172 I paid shipped out the door. The other reviews on the internet were not kidding this thing is tack sharp wide open edge to edge and I love the focal length in that I can simply step a step or 2 closer to my subject and it makes a great portrait lens or step back a few steps and get a bit wider angle. All my lenses (18-55,28-105,50mm 1.8 and 70-210 F4) serve a primary purpose in my gear bag and I think the 40 will fill the role of street shooting lens and then if I need portrait work my 50 can do that and then depending on my needs for a zoom the 28-105 or 70-210 can handle that chore and last but not least old trust 18-55 kit lens will probably stay near the 18mm end for most of it's life with me now so if I need something a little wider than 28.
TL;DR the 40mm is the perfect walk around lens and is sharper than just about everything else in my gear bag wide open. I'll post a detailed review in the review thread soon complete with some nice shots and a real thorough usage. It's big test will be Medieval Times in Toronto this weekend it should perform pretty well even in a dimly lit theater