The new google trends service shows some interesting data on usage of e-government sites. When I last looked at this a couple of weeks ago there was no scale on the y-axis, but they've fixed that now. There are a few caveats about the data - it involves some estimations and normalising, but it looks pretty close to what I think are the right numbers based on my experience of the UK sites.
Here are a few graphs. This first one shows 4 of the main sites in the UK. Direct.gov attracts the most traffic - at something like 170-180,000 people a day. The inevitable huge drop at Christmas and then a bounceback much higher - expected for hmrc.gov.uk with tax return time at the end of January but less expected for direct.gov.uk (which keeps the traffic unlike HMRC)
And here's direct.gov compared with its US equivalent (usa.gov, which used to be first.gov) and also the IRS site. Practically no one visits usa.gov - less than 20,000 a day (in a country of 300 million). The IRS site peaks in the run up to tax time in April as you'd expect but the figures aren't as high as i'd expect.
And another showing some other national portals - not a lot of traffic really, in the scheme of things (and perhaps versus the total cost of service provision)
And, to feed the e-government is dead argument, here's one showing how often it's searched for over time. Not dead but definitely decaying.
And another one for "self assessment" - showing how search traffic has multiplied each year but only in January with a minor (and declining) peak in September as you'd expect.