I know I've already posted this in the IXUS 75 thread, but in case anyone is interested and hasn't seen it there... apologies for the repeat!
Many of the Canon PowerShot and IXUS cameras can be given a large number of extra features using an add-on firmware called CHDK. This doesn't replace the existing camera firmware but lives on the memory card and gets loaded in, so it's completely safe to use. The extra features include being able to use RAW mode, create custom ISO values, fiddle with exposure times, an extra display mode which displays what areas of a picture will be under or over exposed with current settings, a scripting language based on BASIC which allows things such as time-lapse photography and motion detection, and a whole bunch of other bits of stuff which I haven't yet investigated.
The main website is at
http://chdk.wikia.com/wiki/CHDK, and the IXUS 70 (aka the SD1000 in US terms) is one of the supported cameras - the IXUS 75 (SD750) is currently only beta. More info at
http://chdk.wikia.com/wiki/SD1000
I've just popped it on an IXUS 50 and it's given it a new lease of life - right now it's taking 1000 shots at 3 second intervals for a short timelapse film.
Might be handy for those wanting a camera to try out some experimental photography without splashing the cash.