6 month rule
The six month rule does seem to cause confusion these days. My understanding is you can't attend an OD if you attended an OD (not just AD) in the last six months. The last OD I attended (Nov 2010), the recruiter said if anyone had dropped off their CV at an OD in the last six months, they weren't eligible to apply and were asked to leave. It does seem harsh, this is why I think it's better to attend OD's where the numbers are low, at least everyone gets a chance to progress to the AD, and you're not just being assessed on your CV/picture/30 second interaction.