No, especially if it will do what you need, and last long enough to make it viable until the next forseeable upgrade.Isn't it a little wierd to be buying a used computer?
The '08's can hold their own, and depending on the specifics, can actually outperform the '09's (i.e. a 2.93 '09 Octad is faster than the base '08 @2.8GHz <notable price difference too>, but the 3.2GHz '08 is faster than the 2.93 '09 Octad for the same money from Apple <refurb '08 vs. new '09>).
And in the case of a refurbished unit, you get all the parts (keyboard, mouse, power cable,...), and a warranty. You can also add the additional Apple Care to it (highly recommended), and the systems have been tested out before packaging (new = POST testing + just beginning to load the OS, while the refurbs are gone through thoroghly).