There is some benefit to having non-arbitrary strings for URLs. For one thing, if you see the text "interslice.com" on a business card or in an advertisement,

There is some benefit to having non-arbitrary strings for URLs. For one thing, if you see the text "interslice.com" on a business card or in an advertisement, you have some reassurance that it is a website. If you just have the text "interslice", the reader needs additional prompting to know it is a website. Likewise, if you see someone's e-mail address listed as "bob@us.interslice.c", you can tell just by looking at it that there's probably something wrong with it -- maybe you can even diagnose and fix the problem yourself. But you can't do this for arbitrary strings, which carry no such redundancy.