How unique/trackable is your browser?

I've just got a "fingerprint" of my browser through the Panopticlick tool. The result is as follows:

Your browser fingerprint appears to be unique among the 389,007 tested so far.

Currently, we estimate that your browser has a fingerprint that conveys at least 18.57 bits of identifying information.

This is a worrying fact; browser fingerprint is a very effective way of tracking users in the Internet. Why should you take defensive measures against such tracing down? This clearly invades your privacy. You probably don't want someone to profile your online trace without your consent or knowledge. If your browser sends out too much unnecessary information (increasing the likelihood of uniqueness), multiple visits to not only the same site but also different sites can be linked. So, with these fingerprints, systems providing anonymous access to digital content, digital cash become ineffective since these methods make an implicit assumption that the attacker does not use the background information available through the communication channel itself.

It should be noted the same browser fingerprinting technique is used to provide protective measures as well. For example, my bank won't ask for additional credentials when I log through the browser I use everyday, but when I log in from a new browser/new location/new computer, they will ask for additional credentials. The challenge is to protect user privacy without compromising security.

Another challenge is to protect user privacy without limiting the usability. For example, one technique to minimize the risk of fingerprinting is to disable java scripts, but most sites require java scripts to work.

Update [2/2/2010]: The above work allows to identify browsers, but not exact users. Researchers from the Isec lab have devised a method to identify users using social network group membership as background knowledge. It's a two step process:
1. Generate a group membership fingerprint for each users (their thesis is that the collection of groups a user is member of is more or less unique).
2. User history stealing technique to identify the links the user previously visited. Their TR is available here (A practical attack to de-anonymize social network users).