As a few people have pointed out, "slimy" is rather a harsh word to describe O'Reilly's requirement that bloggers create a O'Reilly account in order to get a trackback URL.
Don't get me wrong. I like O'Reilly books, and I like the company.
But I still don't like the practice--it pretty much undermines the whole idea of cross-site blogging and trackbacks. It's reminiscent of the universally-ridiculed "site linking policies" of early corporate Internet presence ("you can't send any visitors to our site unless you notify us ahead of time and get our permission"), and it's not exactly what I've come to expect from a company like O'Reilly. I expect more from them, based on their track record.
So slimy? No, not really. Just disappointing.