I tried posting this in 1.6 Alpha:

<a href="http://www.amazon.com/exec/obidos/ASIN/6305308756/ref=nosim/dannysblogcab-20?dev-t=D2WMCOIPS9D14E">bleh</a>

And I get the Invalid URL error. It will post if I remove the = from "ref=nosim". I'm guessing that the url checker doesn't like an = sign, then more / slashes. They're usually only after the first ? So is Amazon using a bad url, or is there a bug in the b2evolution url checker? I can post that same code in 0.9.1 without getting an error.