When an entity passes through a portal, it is flagged as being unable to use portals. Until it has been out of a portal for that many ticks, portals will not function. It would be nice to have the status exposed. This could be useful for anti-grief plugins trying to prevent players being trapped inside nether portals, among other things.

I'd like to see an addition to Bukkit, Entity#canUsePortals() or something similar.

public boolean canUsePortals() {
    return this.getHandle().portalCooldown <= 0;
}