The latest version of Soulver for iPhone (1.1) is a really nice upgrade to the best iPhone calculation tool.

Reading the release notes, I was thinking 'how does the interface work for all these new features?' The answer is 'so slickly I wouldn't have believed it possible'. Everything just fits in and feels right.

Time will tell, but I still doubt this will replace my Casio for 'real work'. Soulver is the best software only calculator though.