I have a habit of not posting until I have a lot of chapters written first, because I'm one that doesn't like to take too long for the updates.  I used to not post until the whole story was completed, but I've gotten a bit impatient since then.  I would suggest at least having a few chapters written before you post, but it's up to you.

Every author does things a little differently.  With all but my latest story, I had it all written in rough draft and had at least three chapters beta'd before I started posting. 

I don't like the idea of leaving readers hanging with an unfinished WIP. 

Now that I know myself as a writer and that I can and do finish what I start, I feel comfortable posting before I finish a story.  I still like to have many chapters written before I start posting.  Also, I have worked with my betas enough to know that they come through as well.

I personally don't like to let the feedback of the readers push me along with my story.  I have an idea and I run with it.  My betas are the ones I use for feedback about storyline, plot and style.  But, I LOVE getting reviews with con-crit or praise from the readers.

If this is your first story, I recommend getting a couple of betas and content yourself with getting feedback from them only, until you have many chapters written and at least a couple of them ready to be posted.  Or you could use the motivation of not posting until you have a complete rough draft and a few chapters beta'd. 

Ultimately, it's your story and you should do what you are comfortable with. 

Many readers only look for completed stories or read WIP by authors they trust, from past experience, to update quickly and complete a story.    As a reader, that is what I do.  Unless a title or summary sucks me in or a friend recommends something. 

*waves* Hi guest.  I'm guessing you're the same person who was asking about stuff like this on LJ?  Yes? No?
Anyway, I second everything Dawn said.  Feedback from readers isn't likely to be of much help to you in terms of the story. Most people will leave generic "I like it" type reviews if they're enjoying it, and say nothing if they aren't. As Dawn said, reader feedback shouldn't have any effect on how you write your story, or how often you post.   Please don't be one of those writers who says in her author's notes: "Let me know if you like this, so I know whether or not to continue" or words to that effect.   

If you did not see the post on LJ, check here: http://community.livejournal.com/riters_r_us/   for the two discussions on the merits of finishing vs posting as they are completed.  I agree with Dawn that you want to at least know where you are going with the story, and be several chapters ahead before you begin posting.  It's much easier on readers if you keep to a semi-regular schedule of  posting rather than skipping around from two days apart to two months apart.

No, I wasn't part of the LJ talk, though thanks for giving me the link. And when I mentioned feedback, I didn't mean that suggestions would change how the story went, I meant just being able to get what I'd finished out there and know people were reading it and maybe get a response that encourages me to keep going.

Ah, okay. Coincidence then, I guess. LOL   However, as Dawn said, if you've got good betas who are honest with you, their opinion as to how it's going is probably where you should look for your encouragement initially.  Once they've told you it's ready and  you do start posting, then you can bask in the feedback from reviewers.  Don't be discouraged if you don't get a lot  - the number of people who review vs the number who are reading a fic is a pretty big gap.  Good luck!

Hi guest - I prefer getting the whole thing absolutely done then posting once a week and giving each chapter a once over before I put it up.  I do my own beta mostly so I have to review everything a couple thousand times.

speaking just from a "reader only" perspective - it becomes very disappointing to invest time and interest in a story and then have to wait many weeks before an update or to have a work that you really liked end up in the hateful permanent WIP - 

I usually like to wait for several chapters to be posted on a story before I commit my time to reading a work - unless I trust the writer to post regular updates and  what their history and archived work shows.

I'm in the minority.

I'll usually start something, not knowing where the hell I'm going or what I'm going to do with it.   Sometimes, it's more of a help than a hindrance. Whether or not I finish in a timely fashion (or at all) depends on if I run into a writing slump or not.  So I figure, whether it's finished or not, I'll chance it.  Posting it or not posting it won't change if I'm in or will soon be in a slump.    I'll admit it's annoying if you start a story, and it ends up on the indefinite WIP list.  However, there are a few fics I've read, unfinished, that are so brilliant that I would rather read it, unfinished, than not knowing it ever existed.

ETA: Since I don't plan on leaving this fandom...none of my WIP fics will be on indefinite hiatus.  I have time to finish

For some reason, Scarlet, I don't think any fandom would make this interested in its fanfic, either reading or writing, like Buffy did. I won't lie and say I never read a fic outside BtVS but it never captured me like the BtVS verse. The BtVS characters feel so close to me, no characters of any fandom would make me this attached like the BtVS characters.