I think a lot has to do with how much a person promotes their blog. If they are out there networking via the various means of social marketing, then it's easy for people to find them and follow. In this day and age of blogging it takes a lot to get noticed (in my opinion). And it takes consistancy too.
I agree with everything that has been said! I'd also add that a huge focus on giveaways, UNLESS the blog is about frugality/shopping/marketing/etc. where giveaways would naturally make up the bulk of the content, turns me off. If I used to visit the blog for its content and then it changes to every post being a contest, then I eventually stop visiting the blog. I'm all for giveaways on any blog, but good writing is important, too!
Oh my goodness. You guys are right on the music thing. There is nothing worse than not realizing my speakers are on, surfing after my toddler has gone to sleep, and then opening a blog that blasts music at me. Trust me, if it wakes my daughter, I won't be back to that blog again! :)