Paul,

Yesterday I was running a small amount of pvc pipe for another faucet.
I was using an older can of pipe cement(glue) and after getting abot
80% of the job done, I for some reason looked at the bottom of the
can. The use by date is '06', but the glue seemed to be fine. I'm
wondering now if I should get a new can and start over and re-do what
I've got done or if the glue will hold just fine. Thanks.

As long as the cement was still fluid (not gelled) it should work as good
as new. I recommend tossing the cement when it starts to gel, but I have
used partially gelled cement in a pinch without any noticeable issues.

Generally, the cement will keep a long time unless you open the can. Then
the air in the can lets it start gelling. That's why I prefer to buy
several smaller cans instead of a single large one. I can use the small can
for the occasional odd job, and use a new can the next time I need to do
something. The larger cans only make sense if you have a big project, like
plumbing a whole house, or if you do plumbing work frequently.

Anthony