Ignore that post, because it's not true. It may take awhile to get a response...but that post did not help.
1- It's a good way to start. I'd start to send out about 5-10 weekly, and keep track of who you send them too.
2- After 3 or so months, start sending reminders. Not another full headshot, but maybe a postcard with your original pictures, and a few others. It's easy to get something like that made for cheap from vista print.com
3- Send reminders every few months, people will eventually take notice. And I've been called, as have friends of mine, just days, or weeks after I've sent a headshot. It all depends. But really really research on who you are sending your stuff to. Make sure they are a company you like, don't sign with just anyone. Do your homework.
4- Personally, and it may take a lot of time, I don't send a "generic" cover letter. I gear it specifically to the person I'm sending it too. But keep it short. They don't want to read a novel.
5- When you're in a show, especially if they offer industry comps (which any show should) send out another mailer asking them to come. You never know what may happen.
Hope this helps.
The ROSS REPORT is a great source to find out about all the people you'd be sending stuff to.
Now all I see are cute boys with short haircuts in a maze of their own...