Mistake 4: Disrespecting their time
Unnecessary meetings, tight turnarounds, and multiple revisions are all on the "not cool" list of things to request of bloggers. Most bloggers don't make a living blogging -- only the very talented and lucky ones do. Since blogs are usually passion (aka, "side") projects, and you are probably not paying them, cut 'em some slack.
For all you know, the genius behind Dwayne Johnson Central has to pick up his kids from Taekwondo practice before he can post your exclusive behind-the-scenes pics from Dwayne's latest project, "Drivin' & Cryin' 2: Wheels Unleashed."
Above all, just remember that the blogger, ultimately, is offering you access to his audience. An audience that he potentially spent thousands of hours building. If he ever seems standoffish about mentioning something that you consider important, just remember that it could be because of his intimate understanding of his audience. A poorly chosen word could have an effect that you didn't intend. So do your best to defer to the experts (the bloggers) when appropriate.
Extra embarrassing: Giving a hard deadline. It's OK to have a cutoff date. But be flexible, whenever possible.