This is a great move. But it only makes sense after a community with momentum is in full swing. The community experience is the driving force behind reddit/digg/HN/mixx/slashdot/etc successes, not the technology.
Slashdot only went open source after they gained a lead with their own instance of the code. Slashdot only went open source after increasing demand from its community. Since going open source, Slashdot has subsequently gained bug fixes and a much more scalable implementation at reduced cost. However, I cannot name any other instances or derivatives of the code which are active - not even Squishdot Zope clones.
So, if you've got a big archive of posts and a large number of active users then open sourcing your code only entrenches your position by reducing costs.
A valuable observation, but seemingly only valid for frameworks and backends that are merely a glorified CMS.
Much of the web is a glorified CMS, indexed by Google.
If your businesses produces value through human generated content[1], you should share your code to push down the cost of technology, undermining the market for people trying to sell similar but potentially innovative software to your competitors.
[1] as opposed to computer generated content, such as online catalogues or search indices.
and a computer is just a collection of coloured pixels flickering a bit.
In Spain we have http://barrapunto.com much smaller but also using slashcode. IIRC there are also two more instances, one of them in Portugal.
Barrapunto added its own features for a long time, but they weren't incorporated to main branch, and after serious scalability and trolling problems arose, they reverted to regular slashcode.
That's very pertinent because reddit haven't released code to reduce spam:
From the article: There are a few portions of the code that we're keeping to ourselves, mostly related to anti-cheating/spam protection.
Anyone deploying their own instance of the reddit code will have to develop their own protection against spam, trolling and rigged voting.
Absolutely. I'd be much more impressed with a comprehensive API for votes/comments/stories.
Pretty much, I think it would be best for everyone to let people make reddit (or private reddits) the back-end infrastructure of all sites like news.YC, slashdot (just like flickr is a back-end for other people's sites).
This was submitted as a request well over a year ago:
http://www.reddit.com/info/1jhma/comments/
It's interesting that you commented on that thread, saying:
adding the display templates is easy. what i'd be really concerned about is the db load, but that's solvable as well.
We'd certainly do it. It just takes time, and that's a scarce resource at the moment.