Some of this is currently possible with Dare/Syntax via private message or in channels that have the +google flag. Below are a few examples:
/msg Syntax -g 12 ft in cm
<Syntax> 12 feet = 365.76 centimeters
<SecretAgent> -g 12 lbs in kg
<Syntax> 12 pounds = 5.44310844 kilograms
<SecretAgent> -g 100 f in c
<Syntax> 100 degrees Fahrenheit = 37.7777778 degrees Celsius
<SecretAgent> -g 45 USD in pesos
<Syntax> 45 U.S. dollars = 598.006645 Mexican pesos Rates provided for information only
<SecretAgent> -g chinese money to euro
<Syntax> 1 Chinese yuan = 0.102965047 Euros
...and so on. Just about any calculations / conversions google can perform are supported. If you find one that isn't, let us know and we'll definitely try to add support for it.