My only gripe with the lasso tool and popping it on a new layer is:
1) You won't ever get that smooth a crop line
2) If you screwed up and later decided you wanted to add another element of the pic in color, you have to start all over again. Plus if you delete the pic too much, you can go back and fix it without dumping the original picture.
And desaturation works fine, but you can't take it off without undoing everything. Hue and Saturation layer can be removed if it looks bad.
Use the mask on the layer, pic a really small paintbrush and paint it away nice on the edges. You can use a bigger brush to paint away the rest of it later. If you ever go to a company with a design for print or web firm, they won't appreciate the lasso trick because it never comes out perfect -- and once you start working with cutting away the background from trees and flowing hair, you'll see the difference.
Both ways work fine and will accomplish what you need, just use this for reference if you have to do some hardcore photoshop design. All those crappy pictures you see at http://www.gap.com
on their sites and their stores, that's what we have to do... because it needs to be perfect at all times. Sucks.