Once you've installed the script, bookmarking pages in Google Reader is as simple as hitting the F4 key, entering optional comments or tags, and using the Post Item button. If the F4 key doesn't suit your fancy and you don't mind rolling up your sleeves for some minor script editing, you can change the if(e.keyCode != 115) line to use a different keycode. I've found this script incredibly useful for quickly saving bookmarks to read later from one consolidated location—though previously mentioned ReadItLater is a whiz at that sort of thing if you prefer a different approach.
AddTo Google Reader is a free download, requires Firefox with Greasemonkey. Readers using other browsers can get the same functionality in a bookmarklet—just one more way for getting good with Google Reader.