Barghouti is one of the few Palestinian leaders who could paper over the ideological and political gaps between the Palestinian Authority and Islamist groups such as Hamas. That ability, combined with his strong military base and a political stance that recognizes Israel's right to exist, made Barghouti one of the few Palestinian leaders with both the desire and the ability to reach an eventual agreement with Israel.
It is not yet clear whether Barghouti was betrayed by Palestinian rivals who were threatened by his assent. Israel may have also arrested him in order to bolster his standing among the Palestinians -- spending time in an Israeli jail is a good way to increase street credibility -- in the hope that this raises Barghouti's position versus that of Arafat.
Watch this situation closely!
DaMan