Alright, even though it seems likely no one cares because I'm sayin' it:
I personally feel that custom items should be worth challenging someone for a la the Bjuu, it's exactly as everyone's been saying. The people tend to go inactive or just hide it away like cowards.
However, custom items, just shouldn't be touched. I just don't think it's fair to take an item someone may have spent hours working on and/or fitting into the Naruto-verse, plus, we'll have that one OP character that preys on people with custom items, and grow insanely powerful.
JUTSU/ETC
Both canon and custom should not be challengeable. I had someone once beg me and then get very upset because I refused to teach him Mind's Eye of the Kagura IC.
Besides, this means that more powerful players can wail on the weaker and inexperienced ones, or the old an inactive ones to learn more powerful techniques if they can. It takes the originality out of SL. We don't need 50 people running around spamming Hiraishin or using the most powerful summon etc. etc.
Final Verdict:
It should only work that way for Bjuu and Canon Items, I can understand that it's great you guys can challenge one another. But it's the same thing as having a zone record of say, 50-2-0 and those 50 wins being against Acads.
The weak will prey on the strong and that's not fair. Bocchiere, the most OP character will end up with everything. That's not fair.
Besides, isn't this what claims were meant to be made for?