Putting this here in case I'm the only one for whom this wasn't obvious.
Itunes new "instant" search function is great, except for the fact that it (apparently) does not search track artists (only album artist). Try it yourself on a compilation album or soundtrack. While typing in an individual track's artist name you will get a discouraging "No Results" in the instant search drop-down. This is confusing because it makes you think it doesn't exist in your library.
However, if you hit Enter that will perform a more thorough search and put the results in the main iTunes window, which does include searching the track's artist field.
Like I said maybe I'm the only one who found that confusing. I'm sure Apple did it as a trade-off so the instant results were more instant--especially on older systems and larger libraries. But still, I think rather than "No Results" they should add text instructing the user to hit Enter to perform a more thorough search, because the pop-up window as you're typing gives the impression that those are the full search results.
Otherwise, I'm liking it!