I sometimes spend a long time working on answers to questions (eg, weeks or months). Sometimes I reach a "milestone" when answering that still isn't a complete answer, but may have the following properties:
It lets the OP know that someone's working on the question and have had some level of success.
It lets the OP indicate if the direction I'm moving in is right or wrong.
It lets the OP say "someone else answered this somewhere else, I no longer need the answer".
It may entice others to contribute more to the answer, help me with my answer, or make corrections to my milestone-not-answer.
Sometimes, I just get tired of working on a question. By posting a milestone, people have at least something ("this is as far as I got, maybe someone else can get further"). However, it's not always permanent. I may do more work on the question and want to post the additional work.
Solutions I've considered:
Do nothing until I have a real answer. Despite what I think, the steps I'm taking and milestones I'm reaching are not of interest to others.
Post the first milestone as an answer, and then update the answer with each new milestone. This lets the OP (and others) get information as quickly as I can find it, but it appears that the OP and others wouldn't receive notifications when I update the answer.
Post each milestone as a different answer. This makes me cringe, since it could be seen as an attempt to garner reputation.
Post the answer on my blog, link to my blog, and, in the blog entry itself, ask people to subscribe to the RSS feed for that entry, so they can be notified when I update it. I've read other posts on this subject and know it's acceptable, but it seems really unfriendly if Stack is a "source of knowledge" instead of a "source of links to knowledge".
I can provide specific examples (quite a few of them in fact) on request, though I'm looking for a generic solution.