New members (without three posts approved) have to go through a moderation queue. This allows us to let spammers reveal themselves so we can ban/delete them. Approval time varies based on our schedules. As an example, in the past few weeks I've moderated posts on:
Feb 28, March 4,6,8,10,11,13.
I delete about a third of the new members due to spam; most of these are not computer programmes but people in high-technology, low-income places like India, so they manage to bypass the usual sorts of Turing tests that will snag a programme. Some of the posts are seemingly on-topic— there was a recent one talking about string gauges that suddenly veered towards credit ratings at the end (including a link).
Could be worse:
NeoGAF (video game forum) approves new accounts every 6-12 months and new members are on probation for three months and banned at the slightest provocation.