for time-lapse photography I can also highly recommend using the CHDK framework with your latest powershot. read their wiki there : http://chdk.wikia.com/wiki/CHDK
The basics of CHDK is that it is like a mod of the firmware, but without actually changing the firmware (ok they explain better than I do lol). Once you have it running on your sd card, you can then let it run scripts with limitless possibilities (you can modify them and also write your own in LUA, a fairly straightforward language) : override the stock ISO values, do bracketting for HDR but also White balance bracketting, focus length bracketting, motion sensor, you name it. It's pretty awesome and imho it's why canon point and shoot cameras are the best on the market. Alas it is not available for DSLRs, although there starts to be some fancy smartphone apps which may be nice too.