I lived in Seattle during the WTO protests. There too a percentage of attendees were interested in mayhem rather than issues, particularly, by vandalizing the property of people and businesses that had nothing to do with the WTO.
I think that it is inevitable that troublemakers will show up. Whether that is entirely bad or good I won’t say.
Let me change direction for a moment. To effect change, OO needs a carrot or a stick to go with its demands. So far OO has gained national attention, by making the government of the City of Oakland uncomfortable. The concept of occupying an empty building was interesting; with a twist, it can be an effective stick. Another stick that OO has, with its remaining public support (It has to be admitted that some support was lost in the invasion and damage of City Hall, whether or not police tactics drove the group in that direction.), is that it can organize the public to vote differently from usual.
When the OO takes action, it should take action on a local, state, or national building. If it is local, OO should consider occupying or blocking the main entrances to City Hall. If state, OO should consider occupying or blocking the main entrances to the State building on Clay Street. If national, OO should consider occupying or blocking the main entrances to the federal building on Clay Street.
Beforehand, OO should issue a press release that the group itself is firmly against harming people or damaging the interior of buildings and that the police should arrest anyone who chooses to do either.
Additionally, the group needs to provide criteria for when the action will end and to state its primary local, state, or national demands for the event.
In addition to targeting buildings, OO should focus any action on the votes that allow a particular local, state, or national politician to remain in office. OO should ask the public to pledge to fight corruption by refusing to donate to the Dems or GOP this year and refraining from voting for an incumbent or candidate unless they pledge to fight for OO’s resolutions. Politicians will not give California or Oakland a second thought unless they see drop in campaign contributions and fear the loss of votes. They threat must be significant if it is to overcome the power that corporations and other groups have (esp. thanks to the Supreme Court’s ruling on the Citizens United case). The public should be encouraged not to fear the consequences of splitting the vote. In the short term, it may bring a less savory politician/ party to power, but it is the one way to force the opposing party to change.
One more thing. If OO recognizes the damage done to its reputation by too many punks, if you will. It may help for OO to self-police its demonstrations. OO might try this at the next action: ask for physically intimidating and courageous (but unarmed!) volunteers to (wear armbands?) and intervene if they see anyone intentionally knocking over a display case or using spray paint inside an occupied building.