This makes me think that there are really two types of scheduled tasks

in Drupal; those that need to happen even if the site is inactive (sending a mail queue), and those that only need to happen if people are visiting the site. Poormans cron does a great job of the latter, but

can't guarantee the former on a low-traffic site. An elaborate but ...

Not even I have such a low traffic site that poormanscron doesn't work. I currently have two sites sending out mailing lists with poormanscron, and they are relatively small user bases (59 and 230 users respectively, currently 61 and 1022 nodes respectively) and the recipients get the mailinst lists just fine, albeit sometimes a few minutes later than anticipated, but does that really matter? Kobus