Interesting graph over on Swivel showing the proportion of people in the US using e-filing for tax returns.
Interacting with government/local government via the Web is really an idea who's time has come - and not a moment too soon.
The interesting thing about this graph is that as an adoption curve it's not that steep. You would think that network effects would have resulted in a steeper climb - as more people e-file, tell others how easy it is, they do it, tell others, etc.
I remember seeing some data on online banking back in the early 2000s and you could clearly see the rapidly increasing adoption of that service. My guess is there is probably a lot of built in inertia - accountants you have always used, not trusting some of the early services, cost.
I'd love to see data on paying parking tickets via the Web - that's a service I have been using a lot recently :(