As others have noted, the EFF Panopticlick is the better service.
I just spent far too much time playing around with this, on an extended lunch break. I note the following things:
- You had better disable explicit tracking services (Ghostery), or it all doesn't matter anyway.
- Fonts are a big factor. Fonts are identified through Flash. There is a configuration file "mms.cfg" that can disable this. The location of this file depends on your operating system and on your browser - it took me a good half-hour to find it for my particular configuration.
- However, even after disabling fonts, and even using a "user-agent switcher" to look like a Windows/Chrome combination (instead of Linux/Chrome), I was still uniquely identifiable. The biggest factor were my language preferences, the list of plugins, and the precise browser version. Refusing to report system fonts was also pretty important :-/
In short, there's not much way around it - if you include other information available, like your IP address, you will be uniquely identifiable, and trackable across websites.
What is missing from this picture: Browsers provide an "incognito" mode. This mode needs to be extended to provide only absolutely essential information to the server. The server needs to know roughly what level of standards support you have (e.g., "Mozilla/5.0"), and what language to send content in (one language, not a list with weights). Everything else could be omitted, and virtually all websites would work perfectly.