Just a collection of screenshots of major change in AO to guide you through the years...

Apr 28, 1998:
http://img153.imageshack.us/img153/328/apr2819989br.jpg

Jan 25, 1999:
http://img357.imageshack.us/img357/3...n2519992kq.jpg

Apr 17, 1999:
http://img357.imageshack.us/img357/1...r1719991lj.jpg

Oct 06, 1999:
http://img517.imageshack.us/img517/349/oct0619991af.jpg

Jun 14, 2000:
http://img375.imageshack.us/img375/7...n1420009zp.jpg

Jan 22, 2002
http://img523.imageshack.us/img523/3...n2220020wv.jpg - Austin powers style

That's the end of the major styling updates screenshots as not much change can be seen beyond that... as for now....