Based on this Google Experimental Search page, it seems as though Google is testing out a prospective feature for search results - voting. The SERPs show an "up" icon and an "X" icon. If a search result is completely irrelevant for what you were searching for, clicking the "X" icon will remove the result from further similar searches while clicking the up icon will raise that result's ranking.
Furthermore, users would be able to suggest relevant webpages to include in the results. Before you start pondering what a gamed Google SERP page might look like, with horribly inaccurate and spammy results - these experimental features are per-user only. Each user must be logged in and any changes made are for that user only and may be reverted easily.
Is it permanent?
Your changes will be applied each time you search for the same keyword(s). There's a link at the bottom of the search results that lets you view the results in their original ordering.
But how useful could this be should it ever become a feature, if the feature remains per-user only? It only seems like it would be useful if you search for the same keywords quite often. My searches are highly random with my last few searches being "iphone tinyproxy + tether", "corvette zr1", "cool bottle openers" (yes, I found one), "svn bus error" and a phone number of a missed call. As such, I don't think this feature would prove useful for me.
Would you use this feature should it ever come along?