For my A4, EVERYTHING is covered... just about.
I expect before the end of my lease, I will need to replace a set of tires. BUT, the service agreement includes a set of brakes, at least one alignment, wiper blades, light bulbs, all oil service, everything else that's included in 'regular maintenance' (ie. regular inspections and lubrications of all the bits n' pieces). It's the most comprehensive program of its kind I believe (4 years, 80,000 kms).
What's it worth? Well, when I had my BMW, the service intervals were much more frequent than they are now. Seems to me I ended up needing 2 services per year (one oil $110 and one "Inspection I" or "Inspection II" which ranged from a few hundred to over $600).
It's so nice to know that no matter what happens to the car, it'll be taken care of -- no surprises at all (and incidentally, the mediocre Goodyear RSA's that came standard seem to be wearing well).
When shopping around, my cost analysis spreadsheet comparing all the different cars I was carefully considering showed that for the Audi, the maintenance and low insurance costs tipped the scales in its favour over the Honda Accord 6 speed I was also considering.
That surprises me about Lexus. Didn't they used to offer the free service?