Baker's Yeast vs Dry Yeast?

I started using the pound of baker's yeast about a month ago. I just
started 
another Italian loaf and noticed that the sponge did not rise, or even get

puffy, as I expected. Sure there were one or two bubbles that propagated
to 
the surface, but that was after 6 hours. So I started to wonder whether
the 
yeast is still good, bad or ugly. This also made me realize that another 
good question to ask in this thread is: is baker's yeast any way better
than 
instant dry yeast. So here are my questions:

[1] how do you know when your brick of baker's yeast has met ended its 
usefullness?

[2] is baker's yeast in any way better than instant dry yeast. (e.g. does 
baker's yeast add flavor to the loaf?)


-- 
-baka joe
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my bread: http://www.joesbread.com/
my faith: http://www.angelfire.com/ny5/jbc33/