Do credit links stay?

I don’t think any theme dev can really answer that. In order to get even the vaguest idea of whether our credit links are being removed, we’d have to know what sites are using our themes. And that would mean incorporating some kind of non-editable tracking code – which would immediately cause the theme to be thrown out the WPORG Theme Repository and probably invalidate GPL.

Why does it matter any way?

A pro developer should know how many times the theme has been downloaded, plus how many backlinks they have from them sites (Google webmaster tools).

Just curious.

Knowing how many times a theme has been downloaded is one thing. Knowing if it has been altered on any one of a 1000 sites is another thing entirely. One of my themes on WPORG has been downloaded over 67,000 times. Personally, I really have neither the time nor the inclination to start checking out all of those sites.

As for backlinks, quirm.net about 18 themes currently available plus a number of plugins – one of which has had over 100K downloads alone – all of which are released with credit links and all of which allow the site owner to remove those links. Quantifying how many of those downloads result in live backlinks would be a huge job and, as I said before, why bother? The SEO juice is likely to be minimal given that each of these approx 250K sites will have content that is totally unrelated to quirm.net.

If you’re creating themes just to get backlinks, I wouldn’t bother. especially if you also intend to support those themes properly. The return in backlinks doesn’t come close to covering the outlay in work,

For those also wondering.. I just found out from two developers the average is only 50%. Lot lower than I thought.

I think that’s a fair estimate. If asked to guess, I’d have said around 50% based on a rough assessment of how many users have the necessary technical skills. FWIW, we get very few support posts here asking about a plain credit link. When people do ask, it’s usually because the credit link is encoded or obfuscated in some way – in which case we normally recommend that they drop the theme altogether.

I have seen a few open source sites (not particularly WordPress) where if you remove the copyright notice at the footer etc, the site will not function and display an error instead such as “License Violation”.
But I doubt there is a way in reality for the developer to be notified of a copyright removal.