Instarchive works as advertised:
There’s been a lot of talk about Instagram lately. We’re pretty sure the sky isn’t falling, but you should always have a backup, so we built this little tool for you.
It’s called Instarchive, sign into your Instagram account and we’ll send your photos down to your computer in a convenient zip file. It's quick and easy, we hope you like it.
I just did it. It was quick and it worked flawlessly.