There are lots of reviews on this so I'll be quick and specific; my wife had an Ixus 40 before this and it wasn't great in low light, she often got blurred shots and the battery life was poor, though she did love the small camera size and pics in good light did come out well. I got her this by way of an upgrade and WOW!

It's great in lower light (higher ISO), the Image Stabilisation means she gets fewer blurred shots and the battery life is WAY better. The face detection is also really good as you can now give the camera to Granny and not get a shot with blurred people and the wall behind perfectly sharp. The screen is also bigger than older models so Gran now stands a chance of seeing it, too.

I use an DSLR myself and I'm still amazed by the picture quality that comes from this little marvel, it is amazing for such a small bit of kit. From an upgrade perspective the old spare battery, case and memory cards from the Ixus 40 all fit.

Downsides? The wide end of the lens range (38mm equiv) isn't that wide but it does suffice. Other than that it's tough fault at this price, size etc. Previous Ixus XX users - it's time to upgrade!