You guys are killing me. I have a 16 F/1.4 and I'm debating on trading it for a 10-24 because I mostly do landscape shooting. However, I live in the Vancouver area where is rather soggy for 5-6 months out of the year. The 16 is pretty wide, but clearly not 10-15 wide. It's sharp, and I do like using it for wide aperture shots particularly in low light, but I really do miss having an ultrawide lens having moved from Nikon and giving up my 12-24 Tokina.
If money was infinite I'd have both. I could do the trade, but I'm sure that I'd then regret it somewhat after doing so. I could stick with the 10-24 and get a 35mm F/2 for WR, and that's tempting, but still, I wish I could in no uncertain terms get a "dude, just do the trade if you have a willing trader" from the majority of folks. It does seem as if people fall on both sides of the fence, but that's often due in part to them only having one or the other lens, and not having owned both.