Well, the new version of Windows is (apparently) due in 2009, with another version of IE to worry about - and requires a meta tag for compatibility - which will then hopefully end the need to code for IE 6.0.
So, 2-3 years seems like a good time frame to me.
But many things will be a lot more difficult in the future, anyway; the need to code for mobile devices, a large range of resolutions. I think that as the Internet grows, the job of designing for it becomes a much more difficult task.
More space, more power, more demand and more possibilities. I actually quite enjoy the challenge of trying to make a site or web-app as 'elastic' as possible, though, so I don't really mind at all. Still, IE 6.0 makes me squeal like a pig.
Edit: Also, I use
Blueprint, which is a CSS 'reset' package that solves all the Margin, Padding and Typography issues across all browsers, and makes them look the same.
It also saves a lot of time going over the same mundane CSS, and so gives you time to concentrate on other languages and increase your knowledge in more areas. At least for me, anyway.