A DimVar (Dimensioned Variable) object attaches real-world units (any combination of mass, length, time, etc.) to otherwise normal numeric variables. Math operations performed on dimensioned variables will automatically perform dimensional analysis to ensure that units are consistent.
In my experience this tool has helped me reduce units-related errors, has made my code much easier to understand, and has also generally sped up my work. It is also very handy for day-to-day unit conversions and other small tasks.
Recent feature additions:
-Easily switch to using a different base unit system and work in any base unit system you like, e.g. English units (default is still SI).
-Added fuller functionality to several methods.
-Sped up and/or simplified several methods, some significantly.
-More methods, including plot, disp, num2str, and others.
Rob is responsible for the first iterations of this submission: http://www.mathworks.com/matlabcentral/fileexchange/10070