Lighter = better in most cases.
In the early/mid 90's things got silly light, manufacturers were pushing the limits (and sometimes exceeding them) of how light frames & components could get.
I think that as the popular riding styles changed (think of modern freeride, all-mountain, bike park stuff) then strength took over from lightness.
Nowadays lightweight is high up on the agenda again, partly due to carbon and composite technologies, making things strong and also lighter (and expensive).
Any weight shaved off your bike is a good thing, it's just whether it is cost effective to do it, besides, there are always those pub bragging rights over who has the lightest/blingest/costliest bike
imo you're better off doing more riding than worrying too much about bike weight, rider fitness generally is a much bigger factor than a couple of pounds difference in the bikes weight.