Yes, a Soft Home Button for iPhone has been released by IPhone Cake.
This is the source: iphonecake.com/src/all this is the source for all apps
iphonecake.com/r.xml this one is for english apps
I installed it on my 1.1.3 and it is working fine, no more pressing the home button and wearing it out, not that I heared of any worn home buttons yet.
You can move it anywhere on your springboard. It does however position itself in the top left corner after you respring. You could just leave that position blank on all your springboard pages. You can not click through it of course. I do like it allready very much. I am uploading the icon cause that's all you see anyway plus the whole app for anybody that want's to install it manually. Enjoy, I am
Edit:
It does overlay the soft home button on all your open apps. You could also, as seeing the button on everything, just make the button transparent and put it in an corner and you get a hot corner. Or put it dead middle of the screen, cause most apps have some buttons on corners or near by. But if you put it dead center could actually work for most apps.
And if you feel I helped, please hit the thanks button.