com-o-destino?.xml

 <h:selectManyCheckbox  id="obstaculos" value="local.obsForm">
    <f:selectItem value="#{local.obsService.obsDefault}" itemValue="#{local.obsService.obsDefault}" />
 </h:selectManyCheckbox>

shine-and-happiness.xml

<!-- Imprime!!!! Such shine! -->

<h:selectManyCheckbox  id="obstaculos" value="local.obsForm">
    <f:selectItems value="#{local.obsService.obsDefault}"  var="o"  itemLabel="#{o.nome}" itemValue="#{o.nome}" />
</h:selectManyCheckbox>

solucao?.xml

<h:selectManyCheckbox  id="obstaculos">
    <f:selectItem value="#{local.obsService.obsDefault}" itemValue="#{local.obsService.obsDefault}" />
</h:selectManyCheckbox>

stack-trace

java.lang.ClassCastException: java.util.ArrayList cannot be cast to javax.faces.model.SelectItem
	at com.sun.faces.renderkit.SelectItemsIterator.initializeItems(SelectItemsIterator.java:195)
	at com.sun.faces.renderkit.SelectItemsIterator.hasNext(SelectItemsIterator.java:135)
	at com.sun.faces.renderkit.html_basic.SelectManyCheckboxListRenderer.encodeEnd(SelectManyCheckboxListRenderer.java:133)
	at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
	at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1863)
	at javax.faces.render.Renderer.encodeChildren(Renderer.java:176)
	at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:889)
	at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
	at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
	at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:461)
	at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
	at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
	at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
	at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
	at javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:751)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:566)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:578)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:221)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1111)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:498)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:183)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1045)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:199)
	at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:109)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:98)
	at org.eclipse.jetty.server.Server.handle(Server.java:461)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:284)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:244)
	at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:534)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:607)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:536)
	at java.lang.Thread.run(Thread.java:744)

java.lang.ClassCastException: java.util.ArrayList cannot be cast to javax.faces.model.SelectItem

<h:selectManyCheckbox id="obstaculos" value="local.obsForm">