First of all, you don't write _great_ blog comments. If you have something really great to say, you publish it as a blog post, submit it to social news sites, and put a link to your post in a comment to the original post. People do that and they are successful. Comments are for losers.
Yeah, that's a lot of trouble to get your stuff (possibly) noticed. I'm sick of this expectation. Technology should address this as a problem. Am I really expected to do a blog to be part of "the conversation"? Am I only listened to when I do the social media dance? I don't like this world.
Something needs to replace the blogger/commenter dynamic. Something that puts people on equal footing by default. The blog dynamic too easily devolves into a high status/low status game.
Everything has it bounds though. There is a point where a comment goes from well thought out and detailed commentary and into the realm of long winded rambling nonsense or expository blowhardedness. It should probably be just long enough to make your point.
There's something to be said for being able to communicate clearly and succinctly.
I do see pg's reasoning here, but I don't necessarily know that I agree 100%. Yes, it's true that longer comments are likely to have more thought put into them. And that shorter comments are likely to have less thought put into them. However, I oftentimes find that making my comments brief takes more thought than writing a long comment.
WebKit has a great feature that lets you just drag the lower right corner on any textinput. I use it in Chrome all the time, I hear it's in Safari too.
On second thought ... Arrgh!