The downfall is you have to have a warm engine to maximize efficiency. Upto last fall I only lived a few miles from work, so the warmups didn't always happen. To compensate I just used mima and dumped a lot of the charge. My current commute is about 15 miles each way on a quiet country road, so I usually save a bulk of the charge for my trip back home.
2000 DIY Generic GT15 Turboed Silver Insight, #5550
Pioneer DEH-X6700BT 4X Polk Audio 6.5", 2X Aura AST-2B-4 Bass Shaker, Stealth Box Sub
Mima #47, BCM Gauge, Ford Hybrid Escaped™ custom 144v 11AH battery pack w. 20% current mod, Matiz rear springs & Monroe shocks, 25mm rear wheel spacers & Blasphemer™ spat cutout, single cone tranny mod