Not in Safari, but there are other browsers like Terra (http://itunes.apple.com/us/app/terra-web-browser-tabs-full/id394704159?mt=8 http://itunes.apple.com/us/a

Not in Safari, but there are other browsers like Terra (http://itunes.apple.com/us/app/terra-web-browser-tabs-full/id394704159?mt=8 http://itunes.apple.com/us/app/terra-web-browser-tabs-full/i...) that let you select a User-Agent. Sites that do this are pretty much the only reason I have Terra on my iPad.