In the very beginning, I'll probably tweet and post on FB as frequently as possible, usually as often or more often than I write articles on my sites or blogs. After a few months, that dies down and I'll tweet for giveaways, new articles, and special offers. I mix it up with Clickbank products pertaining to the blog's niche every once in a while, too. I'd say once every day when you first start out, and gradually decline from there so that you don't get burned out. I never go any less than twice per week to maintain earnings, though.
Post as much as you'd like in the start to get a decent amount of followers/friends. After that, just post content at least once a day and at most thrice a day to keep your account(s) up to date. Any more than that would be considered annoying or they might see you as nagging and unfollow or unfriend you.
I think as long as you don't flood their pages in a short amount of time, it will be okay. People will understand if you have a lot to share, and if they follow you already, they probably like what you share anyway so they will most likely welcome it.
I try to update once or twice per day. I think some people post too many statuses. I also think people find it more acceptable to post more often on Twitter. There are days when I do post more than usual.
I say, share as many thing's as you would like. Facebook and Twitter are social networking sites, so people cannot get annoyed, simply because you post alot or send out a ton of tweets. I have people on my Facebook account, that send out stuff to friends and fans throughout the entire day! If they have a problem with you sending out stuff, than they dont need to be on a social networking site period!
I believe that social media is actually one of the harder things to saturate. Your presence at a time that you post an update is only going out to the people who are online at the time. Twitter makes it a bit easier to interact with users while Facebook is essentially pushing a garage sale sign into the ground and hoping people notice.
Your presence is only polluting followers when you find that your hits decrease as your tweets increase. It should always be the opposite. you should see some sort of traffic after posting to twitter or facebook even if its marginally small. The points is, you don't need to push information onto your social media 100% of the time but you do need to engage the audience and with the ease of direct messaging and connecting via Twitter it won't pollute other's streams.
I update really as often as I upload new content, which is to say, you need to be predictable and consistent (I post a schedule on my Facebook back to let people know what they can expect from me, and people seem to like it). As filler, I maintain a discussion or debate or start one, and update a few times a day via twitter. Engaging and involving your audience is a great way to become likable to a crowd.
I think most people on social networking sites have learned rather quickly to ignore content which doesn't interest them, and slow down for content that does. As long as you're not triggering the "Yes, I've seen that post 5 times in the last week" effect, you should be fine.
At least for me, it's only the highly repetitive or highly off topic content that gets annoying.
Like many things in IM it depends on the niche, but in general I tweet like 10-15 times per day on new accounts, and 4-6 times per day on older accounts. I schedule my tweets so they appear in both EU and US time zones' peek hours. Now if my niche was be fun related it would be an entirely different matter. Fun sites can post/tweet virtually as many times as they like, they will lose some followers but gain 3* as much