I try to use the 2-minute rule when new "stuff" appears whenever I can. Obviously the context matters - if I think of a short computer task while I am in the car, all I *can* do is grab my PDA and record a quick voice memo.
Neil - The 2-minute rule is meant to be applied as you process stuff (that is, when you are using the workflow diagram to work down you inboxes). There will be times when you won't have 2-minutes and you will have to follow a 30-second rule but you may find times when things are a little more relaxed and you can follow a 5-minute rule. It all depends on your situation at the time.
I also highly reccommend that you get all you inboxes to zero at least once every 24-48 hours. I know that getting them all to zero is on David's weekly review list but in reality that isn't part of the weekly review, it's just part of getting ready for the weekly review. The weekly review goes much better if you already have all your inboxes regularly emptied.
re: applicability of the 2-minute rule to romance:
It depends upon whether you are Collecting, Organizing, or Processing.
(I don't iintentionally apply it to Processing, but I have been surprised on occasion)