I have quite a few sites where google relies on the meta & alt tags.
I've been optimizing for a lot of small keyword combinations lately and Google is loving it. We don't get much traffic from these but it adds up and it's targetted.
Each page on my sites has a primary keyword. In the meta and alt tags we include all the possible variations: widgets online, widgetsonline, widgets on line, widgetson line, wiget online, wiget on line, wigetonline, widget online.com, widgetonline.com
Because widgetsonline is so small and there aren't many pages in the database with widgetsonline, google uses the meta tags. Also, these pages are being picked up and displayed in the SERP's midupdate, which I've never seen before, but I guess is the "everflux" phenomena.