If you want to "just start, already" but have an open format, somebody somewhere recently mentioned the locally installed wiki-ish note database and editor Zim. As I recall, they do/did tech support and started using is as a simple, local way to maintain a personal database of references and notes-to-self.

I was curious and put it on one old machine I've been using a fair amount, recently. So far, I like it, although I haven't gone very deep into its features (not that the feature set is necessarily that deep, anyway).

http://zim-wiki.org/

P.S. Just saw your "already invested in Vim" comment reply, so maybe you are looking for something a bit more technical and less "integrated" than this.