It seems Google has begun/is continuing the process of rolling out Google Compute to Toolbar users. If I recall correctly, this was actually available for a couple of years. You could manually install the client, and there was talk awhile back of installing it on the toolbar. This morning is the first time I've seen this show up here.
What is Google Compute, you ask? From the FAQ:
Google Compute is a new feature of the Google Toolbar. The goal of Google Compute is to make a contribution to science by enabling Google Toolbar users to easily donate their idle computer time to worthwhile causes. The Google Compute version of the Google Toolbar detects when a computer is idle and puts it to work on complex mathematical problem from such fields as drug design and global climate modeling.
Also from the FAQ, it seems like this will be a staged roll out to Toolbar users.
13. How come I have this Google Toolbar feature but my friend doesn't?
Google is gradually releasing Google Compute to its users, so it is possible that your computer received the invitation but another computer you know of did not. This feature will eventually be released to all toolbar users. If you want to try it out beforehand, you can do so by going to the Google Compute on the Google Labs.
I'm not sure if I they have rolled it out to users of the new Beta only or not. I only seem to have it on a single machine which happens to be running the 3.0 beta. I don't have it on two other machines running the 2.0 or my tablet running the 3.0.
The interesting thing is, I can't seem to find the Double Helix icon that you're supposed to click to turn it off or anything even mentioning it in the Options. Am I missing something here? I wonder if they're going to make this part of accepting the toolbar in the future?