What's the user agent string for an Amiga browser?  Would be interesting to change a bunch of PCs around here to ID as Amiga....
Great idea:
Firefox: enter 
about:config as URL, change 
general.useragent.extra.firefox to "IBrowse/2.4 (AmigaOS 3.9)" (
source), visit pcpro.co.uk.
PS: Oh crap - you can't change the first part, the 'extra' is just appended. 

"Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.1.4) Gecko/20091016 IBrowse/2.4 (AmigaOS 3.1)"