I've taken to using Google's calculator function quite frequently. Mostly because with the toolbar and the search box in the upper right corner of my browser window, it's the nearest calculator I can reach in terms of clicks and mouse movement; I like to economize (Translation: *cough*lazyass*cough*).
I also use the Suggestions option for the search box (it does the same as
Google Suggest), which allows me to see if I spelled something correctly, or if the first suggestion for a company name is "X sucks" or something like that.
What seems to have been added fairly recently is a suggestion menu containing the result to your current calculation if you entered in a Math expression. This effectively means you can click, enter something like "cube root of pi" (literally!) and have the result without having to click or press enter.

(Note: If you try to double-check this with your own calculator, be sure to set your calculator to Radians. I forgot and promptly got the wrong result. But Google was right.)
Perfection is in the details, and in the convenience.
And seriously, try entering "cosine of cube root of pi" or "30 degrees to radians" or even "thirty meter in feet". I'm currently trying to think of a natural language expression too complex for it to understand. It's not easy.
But, for example, currency conversion doesn't work: "30 euro in dollar" or "convert 30 euro to dollar" does return the correct result on the search page, but it doesn't put it into the suggestions menu. Yet.
Here's dreading the day it says "
Sorry Aran, I'm afraid I can't do that."
Comments
You can do currency
Try: 10 pounds to euros