I've been using GravityForms 1.5 rc 4.2 on a locally hosted WP instance and found that every form it loads will double the port number in the action attribute.
So, say a form would be expected <form action="localhost:8888/dev/...>
Instead, I've been getting <form action="loaclhost:8888:8888/dev/...>
A minor issue - need to remove it manually with firebug - but thought I'd bring it to your attention. I'm using MAMP to run the site and I haven't tried other versions of GF to see if this is a just a release candidate issue.