Jury Nullification Literature of course qualifies as tampering. Any information directed at the jury on the courthouse grounds can be easily and most definitely considered jury tampering. The jury should be left alone to go through the judicial process and make their own decision and not be swayed by this type of literature.
The case of Mark Iannicelli setting up a 'Jury Info' booth outside the courthouse and then providing nullification flyers to jury pool members may be a form of tampering. The issue has been dealt with in court before. Some crusaders have won the right to notify on jury nullification. Iannicelli did not reveal his identity when he was asked to, and was formerly charged for this action. As long as a juror is not influenced, then there is no crime. In these situations, there may be criminal charges laid since there is little constitutional protection.
I really don't believe that the distribution of jury nullification literature should qualify as jury tampering. The reason I think this is because it is not any form of bribery, and it is not threatening a jury member in any way. If a jury member decides to change their opinion after reading such literature, they already would have had a doubt that they were not right in the first place.
Because any American person can be selected to be put on a jury, it is important to understand the responsibilities that accompany that position. Jury nullification literature being handed out at a courthouse would be informative to many and would aid in ensuring a lawful judicial process. I think passing out this literature is less tampering than it is educational.