You're participating on a forum software with more validy checks then any Microsoft product will ever have.
Generally, Vista will have 3 times it 'phones home' to check for validity. Activation (this will never change), when checking for updates, and for error-reporting (which [at least in Beta 1] you can't turn off, however generally most crashes are good to report). Most use a hardware ID hash, which doesn't report what hardware you have, just the hash.
The problem is today, 1 in 3 computers is running an illegal copy of Windows. That's a huge number of people too lazy (or cheap) to spend the $100, or buy a new computer (i've seen $200 computers after rebates now) with it pre-installed.