Re: Blog advice
If its just a blog stick to captchas if you want comments. I, and many others, are unlikely to go through the whole process of registration just to post a comment and the process of registration itself does not stop spammers anyway - the captcha will be doing that as part of the sign-up process.
Anything that gets past the captcha is likely a manual registration to spam and these are common enough that registration forms won't stop them.
So keep is simple short and fast. If the site is made of forums and other membership features then yes signups are not a bad approach; but just for blog comments its overkill.