I do think that gists could be an ideal platform for a more robust todo list, though. It could easily serve as a backend for todotxt [1], for example.
That being said, I definitely think that the best to-do list depends on each person's workflow (the gist approach would be terrible for a real estate person that's always on the run, for example).
Do you use http://todotxt.com/? I hadn't heard of it before, maybe it's worth giving it a shot :)
I have used todotxt in the past and it served me very well. It was originally developed as a simple bash script by Gina Trapani (of Lifehacker fame) and became such a hit that a strong community of developers formed around it, creating interfaces into the todotxt format in a variety of languages and environments.
The fact that it stores all of its data in a single (or series of) simple text file(s) is what makes it really great, as it becomes portable, human-readable, and modifiable if you should find yourself needing to interact with your todo list without any of the tools or scripts handy.
Unfortunately I haven't had a very good track record of keeping up with any of the many todo list applications or variations that I've tried, but every time I decide to try again I start with todotxt.
t add "complete the pricing mocks"
t 1 pri A
t do 1