Generating introtext from document content?

Hello,
I’ve been building an extremely basic plugin that takes the document content, strips away HTML tags and puts n words of it in the introtext-box. It’s not ready to fly yet and is quite hackish..
Anyway, what I’d like to ask is if there’s something like this already? I don’t feel like reinventing this particular wheel.

Valid sidenote
I’m not building the site for myself. Most likely, the guy who’ll take over when it’s stable won’t understand what the field is for, or neglect to fill it even if I mention it to him (maybe I’m being a little bit pessimistic here..)

The reason I want a plugin is I’ve heard that the extra overhead from the summarize-extension can be quite big. Plus, I’d like to actually use the textarea since it’s there and available already.