Google is maybe not completely, "Don't be Evil"

Google's search results are largely "crowdsourced". So, if more people search for "Shoes", and click on a specific shopping site, that will increase that sites pagerank.

Now, there are a number of companies that promise "Search engine optimization". Basically, they have networked computers performing searches, and choosing a link that was funding the optimization. Now, this version of "googlebombing results" is considered a violation of terms of service, and quite simply damages Googles page rank results in favor of "optimized" links.

As more of this "googlebombing" type of marketing behaviour surfaces, Google must modify it's methods of page ranking. One of those modifications, is to attempt to rule out "bots" that are performing automated queries.

It's also, quite possible, that your particular system may be compromised. One of the methods for performing automated queries, involves the use of a botnet type system. I'd recommend checking your system over carefully, for any possible unauthorized software, that may be triggering "unusual search criteria".

I'm not saying that Google doesn't have the capacity to do as most corporations, (ie be evil), but your situation, is more likely an attempt to protect search results from manipulation

 http://www.google.com/support/websearch/bin/answer.py?hl=en&answer=86640

(from the horse' mouth)

Read this first
When Google detects that a computer on your network may be sending automated traffic to Google we may show the following message: "Our systems have detected unusual traffic from your computer network." Automated queries are against our Terms of Service.

The error page most likely displays a CAPTCHA (a squiggly word with a box below it). To continue using Google, type the squiggly word into the box -- it's how we know you're a human, not a robot.
If you don't see a CAPTCHA image or if you continue to encounter the CAPTCHA over and over, try these steps in order:

Check for malware on your computer.
Malicious software, sometimes bundled with other free downloads without your knowledge, can trigger Google to show this message. We've suggested some well-known programs below that can detect and remove such applications. Please remember that we have no connection with these companies and can't guarantee their effectiveness.

Google Pack
The Starter Edition of Spyware Doctor is included free with the Google Pack
Sunbelt Software CounterSpy
Kaspersky Lab Internet Security
Norton Internet Security
MacScan (for Mac users)

If these programs don't resolve the problem, you might want to try an advanced troubleshooting program such as HijackThis.

Contact your network administrator.
If you tried the steps above and haven't resolved the issue, it's very likely that a user or a computer in your network is sending automated traffic to Google. Your network administrator may be able to locate and shut down the source of the automated traffic; feel free to refer them to this page. Sending automated queries of any sort to Google is against our Terms of Service. This includes, among other things, the following activities:

Using any software that sends queries to Google to determine how a website or webpage ranks on Google for various queries
'Meta-searching' Google
Performing 'offline' searches on Google
Once the automated traffic has stopped, the ban on your IP address should be automatically lifted.

If the problem persists, your network administrator should contact us.
If your network continues to experience this message in error, please send us additional information.

If anything this is Google being good, and trying to prevent companies or organizations from artificially inflating their page rankings.

Unfortunately for you, this means that you or someone on your network (or ISP) may either have an infected PC or be part of a botnet, or be engaging in some unsavory search practices.

If you have both a Youtube account and Gmail account, Google will use its cookies to figure out you have both accounts- and will FORCE you to link them.