My 2004 Beetle did the same thing. At first, it was rare & as long as the take was over 1/4 it was fine. But then it began happening more frequently with loss of acceleration for longer amounts of time. Took it in two different times & they couldn't get it to fail, so just kept tank over a 1/4. (The fuel filter was already replaced, & lines were flushed previously... neither fixed the problem.) Last weekend, it had 1/2 tank & failed going uphill on the Grapevine and never really regained acceleration... it would sputter in & out. Since it's a standard shift, it would stall. Filled the tank and it ran with no problems. Took it back to VW and they still couldn't get it to fail, so they replaced the fuel pump. So far, no problems. Will keep you updated.