I think for me it's more that I get frustrated because of the lack of knowledge of people. Many on here have talked about how they are/were complete newbs and they bought great equipment, and have grown into it. Fantastic, that is awesome. If you have a real desire to learn the photography and will actually do it, then by all means get this camera.
As has been said, getting the 40d or even the markII is not going to create a better photo than the rebel version (in this case appx. an xsi). It also, will not necessarily make it much easier to take this better photo. if you go look at the features that make up the difference although useful to some, in most cases the differences are not all that helpful. I mean, the 40d can shoot more rapidly. yeehaw, that will help so much when you want 17 shots of the birthday candles being blown out. The 40d with it's wheel is much easier to change settings rapidly than the xsi. This is exceptionally useful for people who never take the camera off auto (thus don't have those options anyway).
The thing that I become most angry at is the people who should know photography recommending people to get a DSLR or a higher grade one when it is quite clear they don't need that equipment. My wife likes my DSLR, but she finds it much to heavy for her. People often want something they can just fit in a pocket and go, instead they get pushed into buying a DSLR because it's "better".
Again, if you're going to learn the uses of it, and actually do, then by all means, go for it, they (40Ds are nice). If it's just a hobby, don't waste your money. I'm not mad if you do, I just think you made a stupid decision.