What can cause Vacuum loss?

Just tossing a thanks on the tail end of this thread as it helped me go through a similar pain.

Despite staring directly as the warning on my set of vacuum gauges that says "Late valve timing or leak at intake manifold..." it was from this thread I started considering that I might have installed my cams wrong the last time they were out.

I always thought that incorrect valve timing pretty much guaranteed bent valves, but I rode over 5000km with a one link offset and only had problems with cold starting, and low end torque.