FWIW: for what it's worth
XSi: Canon 450D.
SD: Secure Digital
afaik: as far as I know
SDHC and CF both have the same theoretical upper-limit (via FAT32 addressing): 2TB, so we're nowhere near maxing out on capacity in either format. I think, however, that SD has a chance at edging CF out, as it's already the most common format in P&S cameras, and eliminates the problem of bent pins.
I use SDs in my G9, and CFs in my 350D, and honestly, I'd prefer using just the one format between both cameras, so going to a 450D with SD would be nice for me.