I think it's OK to talk about religion as long as you're describing your experiences, such as sharing something God did in your life or a verse that means a lot to you. But getting into arguments about theology isn't a good idea. I've mentioned from time to time the political party I'm affiliated with, but I don't discuss issues or try to sway anyone else to my position. That's just not what my blog is about. I think if I were an expert Washington insider it might be different, but I don't have that credibility. So I just stay quiet on those things. Moms, no matter what religion or political affiliation, have a lot in common, and I try to stick to that.
My first reaction to this question was... there are none! Your blog is your weblog, and anyone can post anything on any topic they want. I don't have to read it if I find it offensive. As for no-no's for myself, I have to use common sense, and like I remind my teenage stepdaughters all the time, and they still haven't learned this... anyone can read anything you post on the Internet. If you wouldn't want someone else to read it, don't post it.
Obviously, keep personal info to yourself unless you want your identity stolen, or worse, a predator to find you and your kids. I'm probably not as careful as I should be, but when it comes to personal info like address, SSN, that type of info, I'm careful. I think this applies to the Internet in general, not just blogging.
Specifically regarding blogging, the biggest no-no would be a tie between spamming and rude comments.
I like to post pics. I'm a mom, so of course, it's CLEAN pix. My kids have seen my blog. If someone else wants to post something I consider inappropriate, whether pix or content, I just don't read it. Blogging is personal. There are very few real no-no's, in my opinion. http://forgetfulone.blogspot.com
I don't like when someone has one of those music players on their blog. (my computer isn't a big fan of them either!) so when I hear my computer chugging as if it's trying to load up music...I make a frantic search for the music box so I can turn it off! I won't return to a blog with a music box.
Petula, some people fuss about long entries taking up too much space on a page, which is why we occasionally use the "more" tag you mention. Posts that contain large images or embedded videos are also an issue for some people--they don't want to take time for them to load unless they click through.
My entries are cross-posted to LiveJournal (where I used to blog), and long posts without "cut-tags" (the "more" thing) are a big no-no there.
That said--I do mind reading posts via RSS feeds that limit the feed to just a few sentences at the beginning of each post, because EVERY ONE OF THEM has a "click here to read more," requiring you to go from newsreader to web browser.