I ran FakeClockup on about 50 3G iPhones on 4.2.1 over the last four months. I suddenly realized it had no positive effect and no negative effects really either. Basically, on an iPhone 3G on 4.x without FakeClockup, you'll feel lag and then your app will slowly load. With FakeClockup, the apps will still load at the same rate except the moving images will load a lot faster. The problem is you only save about a second unless it's an app with a large animation, and it looks a bit unnatural. I don't think it actually drains the battery faster as the only animation for a lot of iPhone native apps is the spinning circle. I never did many tests outside a couple apps and the settings, so you may find it more useful depending on your needs. On the 3GS and above, the lag isn't as pronounced, so it may be more useful. On the other hand, the processors are faster, so you may not need it depending on how many animations there are in your apps.