Why I'm blocking you on twitter

I've been using twitter for about a year and a half now and I follow about 150 friends,  acquaintances, and applications. A little over 2k users of the service follow me, and it seems I get about 10 new followers a day. Over the past few months however, I've taken to blocking the obvious spammy accounts where someone trying to market something tries to follow thousands of strangers. In the past few weeks it feels like I'm blocking at least half of the new followers.

I figure the people behind those accounts (if there really are people and it's not just an automated spambot attack on twitter which I suspect most are) deserve an explanation, so here are my reasons for blocking new followers:

1. You are following more than 1,000 contacts. You could spend hours a day reading twitter while following just 100 people. I usually just check in the mornings and evenings to see what my friends were up to that day -- sometimes it requires paging back 10 times to catch it all and sucks up the better part of a half hour each time. Reading Twitter while following 1,000+ is pointless and likely not being actually read by someone
2. I know twitter is many things to many people, but I like it as a social micro-blogging application with real honest to goodness humans behind every post. I block anything that doesn't have a personal name and doesn't seem like a person writing it. Oh look, a new wax museum in Ohio just started following me! Surely, they don't just want me to click on their bio URL and blog about their new museum, right? Right? Wrong. Humans can follow me, not buildings or organizations or other sorts of accounts that were created to market something and aren't actually being used by a human.
3. You have nothing but URL dumps of every blog post as a twitter update, all linking to your "marketing" or "sales" or "social media" blog. Pretty self-explanatory, but this person is using twitter to merely promote themselves, not to engage with others or share anything of substance.
4. You have a bio that mentions you are an expert on "marketing" or "sales" or "social media". Almost everyone with a bio that mentions these phrases breaks an earlier rule as well, and it's clear they're on twitter and following me for some sort of google gaming reason more than they care what I or 1,000 others might be saying.