Digital Camera Question

[gimmefeedback]

Here's a question for those that are heavy into digital cameras.

I've googled around, but couldn't come up with an answer. I'm also unsure which features really matter, so I was hoping someone w/ a photo background could offer some advice.

I'm looking at picking up a point&shoot canon camera.

There is the SD630, SD700, and SD1000 cameras all in the entry type price range.

Looking at the specs, they all seem to be almost identical (same megapixels, same lcd screen size, same optical zoom,etC).

Is there any real advantage of one of these cameras over the oter?

Here are the specs:
SD630- 6.2mp,3" screen
SD700is- 6.2mp, 2.5" screen
SD1000- 7.4mp, 2.5" screen - $192ish

What's the actual difference between the SD630 and SD700is?
Is it worth upgrading to the SD1000?

I'm not really sure what features are important in a P&S, so I'd like to know what I should be looking for.

Thanks!