Are there any long term effects of donating bone marrow?
To the donator, or the donatee?
Risks for the donor Scroll down to Donating Bone Marrow section.
Other than potentially saving a life? 
The risks are pretty small for donors, but the rewards are huge for the recipients. My best friend is alive today because 15 years ago her brother (then only 11 years old) donated his marrow to save her life. He says it was worth the week or so of pain.