Moderation in meditation for lay people
Daniel Ingram writes a lot about the 'dark night' and working through it. In an interview (Buddhist Geeks I think - sorry no exact reference) he said that dark night will be encountered by


Intense meditators who really go for it - many hours a day over months
Committed but steady meditators who meditate every day for around 30 minutes and maybe go on a week's retreat once a year. Then after 20 years - bang - they are in the dark night


So according to Daniel you don't need to be a intensive meditator to get the dark night effects. You just need to be reasonable committed and practise over a long enough period. So advising lay people to moderate probably wouldn't be effective - at some point they are going to hit something unpleasant. Perhaps the best thing would be to make them aware and give them tools to cope. That approach is one of the major themes in Daniel Ingram;s book.

On a personal note - My practice is firmly in the second category but I have banged up again some crappy stuff. Not "dark night" but crippling doubt and inability to move forward for extended periods. I think it just happens.