The problem with this kind of ad-hoc TODO lists is integration. They are alright as long as you don't try anything fancy but this is inevitably going to happen as soon as something gathers more users. And suddenly you hit a wall in terms of integration and extensibility in most environments. How do I tie in a simple link? Oh, we need links to eMails/files as well. Someone needs more than one kind of TODO. Hierarchical TODOs would be nice. TODO dependencies. Exporters. The list of possible features is endless and every system that does not keep that in mind and plans for it is doomed to fail or only usable for a very small user base, which is fine if that's your goal.