There’s a rather neat screenshot of this Mac OS X calculator program over at the Soulver website. Particularly, it shows that it can (like Google) take plain English questions, such as:

What is 20% off $35?

which is rather neat, and would make a mockery of most of what my Maths homework consisted of if I had a time machine (but I digress).

What would be really neat would be to add a voice interface to that and shove it on an iPhone – forget comparison shopping via taking pictures of barcodes, just pull out your phone and talk to it, and work out those pesky exchange rates (including credit card %age markup), or complicated discount scheme without having to peck around on a keyboard and try to remember how the % button is supposed to work.