1) DO ask your photographer what their specific policy is on taking pictures off of their Facebook pages/blogs. Some photographers encourage it and some don’t allow it. If this is important to you this is something you should ask BEFORE you hire your photographer!
2) DO include your photographer’s name and website under the images (a link would be super nice!). That’s just the polite thing to do.
3) DON’T crop out their logo. Unless you have paid for the digital negatives don’t alter the files in anyway. Most photographers use their Facebook pages/blogs to advertise their work and do so as a courtesy to give their clients a sneak peek. If a client crops out the logo then how will other people know who took the picture? I know that Facebook now often doesn't allow for keeping a logo in a profile photo if not right across your face, so at least follow #2 in this case - thanks!
4) DON’T edit the picture in any way. Taking the pictures is only half of a photographers job. The other half is editing. If you think you can do a better job or want to edit out some of your wrinkles or use selective coloring, please don’t - show and/or tell your photographer what you want!
5) DON’T try to print from the files on Internet. For me specifically I know that the files I upload to my site are too small to be printed in a 4×6 size. It’s not cool to invest in a session and then print the images off of the Facebook page or blog and not pay for prints. Make sure you know how much the prints cost before the session to avoid sticker shock.
6) DON'T just take photos off the Internet and use them for your event or publicity. Just because something is on the internet with no credit or information, doesn't mean that it doesn't belong to someone else. Here's some guidelines as to how to progress in the future: http://lifehacker.com/5992419/the-best-ways-to-be-sure-youre-legally-using-online-photos
Remember, this is how photographers make a living. I wouldn't take from you, please don't take from me. Thank you!