I've been pulling up carpet. The underlay is stapled down and when I lift it, I often am left with a small tuff of underlay and a staple in the subfloor. I've tried removing using a flat shovel, but it isn't getting many of them. Are those little pieces of foam a problem or should I just tap them down with a hammer and lay the hardwood over? I've installing solid, 3/4" hardwood and I intend to nail down.

Best to pull those out, you don't want to install over the little bumps.
I use this scraper with a dull blade, lifts them right out. Available at big box stores.

http://www.doitbest.com/Window+and+pain ... 772845.dib

Thank you for the tip. I went to the hardware store and came away with this tool:

http://www.homedepot.ca/webapp/wcs/stor ... PartNumber

I can't "scrape" the foam staples out of the floor, but I can pry them out of the floor using the corner of the tool. If just leg comes out, they are easily pulled with the hole in the center of the tool.