Same site, a few days later: Don't do it. (Score 2, Insightful)

Ok, but the same webmaster says:

I decided to stop posting backlinks in Wiki sandboxes, the SEO strategy previously explained. [...] In the meantime I'm asking developers and those hosting Wikis of their own to please exclude sandboxes from search engine results (via the robots.txt file). Doing so would shield the sandbox from backlink-postings, and there is no need for it to turn up in search results in the first place.

This sure makes sense, and who knows, maybe future wiki distributions do it by default. (If

<meta name="robots" content="noindex">

would work universally...)