Henry's in Canada has already instituted the $150 price drop on the XSi 18-55 kit. It's at $849, and they've further reduced it $20 to $829. Body Only has dropped to $729.
I'm also told that there will be a sale on the camera in a week or so, dropping more money off it.
The XS will be coming in at $749 in the 18-55 IS kit. I could see its street price at $699.
Canon USA should follow shortly (if they haven't already, no time to check)