For me a big part of my enjoyment comes from the "feel" that the bike has. That sort of "feel" comes from a number of things and is a combination of the steering and body geometries, weight and how the frame flexes to return my efforts or not.
My two favourite bikes are a steel 22 lb single speed road bike and a 25 lb mountain bike. I've also got a 20 lb "budget" roadie and I don't like it as much as my single speed for a variety of reasons.
So I would say that up to a point weight is important but even a light bike isn't going to have that feel if it's the wrong shape. I'd say rider fit geometry is more important than 3 or 4 lbs of extra metal and rubber. But if you start getting up to 8 or 9 lbs of extra metal and rubber then the bike itself had better fit you REALLY well....
