A lesser known feature of Gmail is that it allows for 'flexible' addresses. Example: Your e-mail address is brian@gmail.com, and I send an e-mail to brian+mindsay@gmail.com. This e-mail will still land in your inbox.

Suppose you have to sign up at nytimes.com to read an article. You don't want to use your Gmail address because you know those guys are the lucrative sort and they are probably going to sell it. Solution: sign up with the e-mail address yourname+nytimes@gmail.com. The e-mail will still land in your inbox, and after you receive your registration e-mail you simply create a filter that automatically trashes any e-mails sent to yourname+nytimes@gmail.com

Suppose you want to leave a comment on my blog, but know that e-mail harvesters are going to pick up your address. Just put your address as yourname+alterego@gmail.com. If it gets out of hand simply block all e-mails sent to that address. No biggie.