The new units facilities of Mathematica Version 9 has advantages and disadvantages. It uses Strings instead of symbols, often requires an online connection and encourages the mixture of units into equations and various expressions where they might be less than appropriate.
It is my view that units are part of the data and should only come into play after symbolic manipulation has been performed, that is by substitution at the end of a derivation.
In any case, if you prefer the older units style the ExtendUnits package, which I sell for $30 from links at my web site, retains the old units and has many useful features.
1) The old Unit and PhysicalConstants units have been built-in so will still be available.
2) There is a procedure for generating expressions that have whatever implied input and output units that may be desired. These could then be used in numerical routines without having to carry explicit units in expressions.
3) Custom units can be installed so you can use all the variations desired.
4) Reduced units where some physical constants are specified to be 1 can be used.
5) Decibel units can be used.
6) Units can be parsed into descending compatible units, e.g., Hours, Minutes, Seconds, or simultaneously converted to multiple compatible units.
7) There is a handy palette that gives a quick listing of built-in units (both alphabetically and by magnitude) and constants as well as the routines in the package,