Hello,
I agree that keeping a link back from within a Wordpress them to it's author is
fair. But there has come to light an issue that we all need to be aware of.
Check it out:
WP Sphere redistributing themes with malicious code | Plain Old Semantic HTML
I kill any encoded scripts on any themes I use. But unfortunately - and this is
for the authors protection - when you remove that code, the theme will
collapse. So I stick to "honest" themes from the "official sites".