The first issue is not having a preview button. Here's what Joel writes:
The first problem here is that it assumes that people use the confirmation feature (or an optional preview feature) to fix typos, but with the software that supports blog comments, that's often not the case. Different blogs support different feature sets. Some, like this one, will let you put hyperlinks in comments, add italics for emphasis, and properly support paragraph breaks. Some require you to manually insert paragraph breaks using the appropriate HTML tag. Some let you use block quotes, like the text above, while others don't. And most won't tell you what feature set they support. As a result, without at least the ability to preview your comment, you're writing blind: you take your best guess at what features that blog supports and hope it comes out OK.
Q. Why don't you show people their posts to confirm them before you post them? Then people wouldn't make mistakes and typos.
A. Empirically, that is not true. Not only is it not true, it's the opposite of true.
Part one: when you have a confirmation step, most people just click past it. Very few people reread their post carefully. . . .
Part two: the lack of the confirmation step actually makes people more cautious. It's like those studies they did that showed that it's safer, on twisty mountain roads, to remove the crash barrier . . . . You're better off, statistically, just scaring the bejesus out of drivers so they creep along at 2 miles per hour around the hairpins.
The second problem is that some people misinterpret this comment to say you shouldn't have a "preview" button. Notice that Joe's writing about a "confirm" button, something everyone would have to click. A preview button's not the same: it's optional. Some people do proof their comments, and for them, being able to see the comment in preview form is useful because it rearranges the text. It's like printing out your document and proofing it with a red pen: because it's been rearranged, you'll see things you might not have seen the first time around. Not giving them a preview button makes it harder for them to write well even when they're willing to take the time to do it.
Another place where I'm not so sure the forum design translates well to blog comments, at least where the blog has a registration system, is in showing the existing comment:
Q. Why don't you show me the post I'm replying to, while I compose my reply?
A. Because that will tempt you to quote a part of it in your own reply. Anything I can do to reduce the amount of quoting will increase the fluidity of the conversation, making topics interesting to read. Whenever someone quotes something from above, the person who reads the topic has to read the same thing twice in a row, which is pointless and automatically guaranteed to be boring.
The problem here is that blogs generally sit on the open Internet, and text on the Internet is effectively permanent. How can something so ephemeral be permanent? Because disk drive inventors are busily doubling the size of storage every year and a half, so people archive everything. Some year in the near future, you'll be able to fit the entire contents of today's world wide web in a device the size of a USB flash drive. (Don't believe it? Doubling every 1.5 years means a 100x increase in storage capacity every ten years. So today's 2GB thumb drive may be a 200GB unit in ten years, and a 20,000GB unit ten years after that, and so on.) And, thanks to archiving, that copy of the web will contain each and every one of your blog comments from X years ago.
Archiving means conversations are not like that fluid conversation you have in the corner coffee shop where everything you say vanishes into the air. A better model might be a debate between two people writing letters to the editor in a national newspaper: that's the kind of potential those comments have to come back and haunt you, at least in today's society. Hopefully one day society will shift and people will lighten up about holding others to their written word, but it's not a sure thing. So if you're going to have a registration system that encourages people to use their real names, you should also give them the tools they need to write in a way that will withstand the test of time.