At Color Online, I post daily. Some days I run two posts. I'm truly a scatterbrain, a passionate scatterbrain. Over time though, I've managed to create a schedule and for the longer periods of time, I'm maintaining it. A schedule has helped me and according to our stats, our readers appreciate it, too.
At my personal blog, it's up and down depending on how much time I spend at CO which has been a lot lately. Now that I have a pretty good clip going at CO, I'm looking forward to creating a regular schedule at Black-Eyed Susan's. I'm thinking 3-4 posts a week.
I think readers do appreciate knowing that on certain days you run a particular feature. I read a lot of blogs, and it helps knowing that on certain days so and so is running X piece. I can't check my favorite spots daily but I do check on specific days knowing there is something in particular I want to read.
I average around 3-4 posts a week. I would love to do everyday, but my full-time job, kid and husband get in my way (j/k). I really think that it depends on the blogger and what you are trying to accomplish via your blog.
I blog whenever I can... usually if something big happened or I have an opinion I want to air. With my book blog, I review the books once I've finished them and given them a few days to stew in my mind. Otherwise, I have other books to review (children's books and books I've purchased). I've recently introduced a new chapter to 'My Reading List' and it's a 'In My Shelves Monthly' where I tell you - the follower - which books I bought, where and at what price. Seeing I purchase my books from either charity stores, bargain/sales bookstores and second-hand stores, you never know where I'm going to get my books from one month to the next. Also, you never know what editions I'll stumble across either. So, that's why I've included this little monthly 'hey look what I found' piece. I've even tagged it as 'In My Shelves Monthly' so you can click on it on the sidebar and look at them all at once from month to month.
I had the advice to blog once a day, especially to start, because that is how you build up a reliable reader base (more than once can become overwhelming). If you either don't have the time or enough to write to fill up one a day posting then the key is to be consistent. Readers should know when to expect a new post and if you disappoint them they may be less likely to return for updates.
To start either one a day or 3-4 posts a week would be a great idea. And if at least one of those posts are a weekly theme/gimmick it may help keep the ideas/content consistent (but that is my personal opinion, not professional advice).
I am so bad about sticking to what I say, but once a week is a good rule. Especially if you have an RSS going to an email out group. Any more often than that, I lose readers.