Different tire and rim widths front and back - Why? Should I replace one? I just bought a Trek 7.2 hybrid bike on Ebay and got the surprise (didn't read the listing closely!) that the front and back tires and rims are different widths. I am wondering if I should give it a try or spend some money on making the front wheel be the same width of the back. Why would someone have different wheels? Here's the configuration I have:

Rims: (Front) Alexrims DA22, (Rear) Matrix 750,
Tires: (Front) Vittoria Zaffiro 700 X 25C, (Rear) Bontrager Select Invert 700 X 35.

Any thoughts on this would be appreciated.
It is ok to have different width of tires on front and rear wheels, I
have a thinner tire on rear wheel as the clearance is low and I
wanted to fit a full fender.
Why would someone have different wheels? -

It is quite uncommon for new bikes to have different width of tires
but used bikes can(as your's is). Perhaps, if the wheel was
damaged/stolen the previous owner may have replaced with what is
available/cheap.
If you plan to change the tire size, ensure that the rim can securely
hold whatever width of tire you are about to install and has enough
clearance for fenders/frame. 
If you bring your bike into local bike shop, they should be able to
tell you if a certain width will fit your wheel. 
Just a tip for comfort - 35mm tires will ride a lot smoother as the
pressure on 35mm will be approximately half of what 25mm tires
requires.