Can Blog Reply Post's that link your website harm your pagerank? Lets say you find 20 PR7 blogs and post in them, and they are all related to your website. Is that organic or cheating?
It's neither organic nor cheating. Such links simply don't have weigth, so there is no way they can influence your rankings or PR.
Unless they are from do-follow comments. However, isn't it better to have more visits from a niche website rather than (potential) visits from people that increase your bounce rate and lessen the time spent on your website?
What if the links are actually in the blog post it self, does that make a better difference? Will that help you rank up?
blog comments in wordpress are automatically no-follow by design unless the admin turns on do-follow with a plugin. A link in the blog post itself might be do-follow. In either case, simply look at the page code to find out if you are do-follow or no-follow.
Yes, you are right, tom11011, But including some percentage of nofollow links are also good in SEO, in this way your back links would be natural.