completely understand ... I am on several open source projects and have attuned my senses when a 'asker' is straying across boundaries; I make it clear that I am willing to help but wont do their work for them and I give myself a time limit (sometimes this is # of emails, duration ... whatever fits) and pop it into my emacs journal so I can get some perspective. This seems to work for me.

I try to remind myself that many times people can be at their wits end and really desperate (esp where data loss and other vagaries strike) but there are the rare 1% of people who for example make feature requests and demand time estimates ... or are not willing to invest a single minute in researching using that great big thing called the 'internet' the basics ... I dont waste any cycles thinking about it and just send their mail to /dev/null.