Homebrew PCBs

>I am just going off the spec sheets for shelf life. I am not sure what
>happens as the resist starts getting old.

     As I understand it (I think from someone mentioning it here), the 
film will go bad from the edges in - oxidation or something and the edges 
being the unprotected bit. Potentially disastrous for a company using 
it's full width in a double roll laminator in a production setting, but 
mostly just an annoyance for hobbyist types. However, I sell things for a 
living and I completely understand your concerns.

Russel has a good point - test it every so often. I'm not sure what to 
look for though, hardening? Poor adhesion? Loss of photosensitivity? A 
color change along the edges and separation of the cover sheets at the 
edges would probably indicate failure in those areas, and should cast 
suspicion on the areas farther toward the center. Information on this 
would be useful to those of us with more than a small supply of the stuff.

-Gary