Open letter to web services companies: When you send me emails that need me to follow a link to respond, don't make me jump through a bunch of hoops to do so. For example, take Twitter. About twice a week, I would get an email telling me that someone wants to follow me. All of these are spammers. In order to block them, I have to click a link in the email, log into Twitter, click a button to block them and then another to confirm. Instead, there should be a link in the email to accept and one to block, and neither should require me to log in. This is not a high-security situation; I wouldn't want emails from my bank to work this way, but for Twitter there really aren't any consequences if someone gets into my email and accepts a follow, or if I do so accidentally. In the end, the easiest way for me to solve this problem was to just terminate my Twitter account, which is what I did.
Similarly, Meetup: I get an email asking me to RSVP. They conveniently provide Yes, Maybe, and No buttons in the email. However, in order to follow them, I have to log into my Meetup account. It's a pain. So, when my answer is "No" (as it usually is), I just don't bother. This can only end up hurting the meeting organizers, and thus ultimately hurting Meetup itself.
For an example of doing this right, take Netflix. Periodically I get an email from them asking when a DVD was sent, or when it arrived. There are appropriate links in the email. I click the right one, and I'm done. No login, no confirmation. One click. The companies who are doing this wrong should take a lesson here.