So.. at the risk of looking geek-like, all of my bikes are weighed on pretty accurate digital scales, old and new.
I always raise an eyebrow when I hear someone talk of `17 lb' race bike in old cycling footage. There's a piece in ITV's 1980 Tour de France coverage that does exactly that when describing a TI Raleigh team bike. Perhaps, with ultra light tubs, copious drilling and a Huret Jubilee rear mech...
My old (mid 80s or earlier) steel bikes range from 19 to 20.5 lbs. I run fairly heavy Vittoria Rally tubulars. The lighter bikes have alloy freewheels and titanium bottom bracket axles - these bikes have Campagnolo Record or Super Record group sets.
I have one bike that I've tried to make light (without drilling stuff) - the aluminium Alan - that's still over 18.5 lbs with light rims, titanium axle and alloy freewheel.
My carbon Ciocc with modern Campagnolo Super Record is 7kgs or about 15.4 lbs, and yes, you can really notice the difference. I's possible to buy a 5.5kg (12 lbs) road bike if you have budget. This is in the ball park of Merckx's '72 hour record bike (astonishingly light for its period), but of course it comes with 22 gears, brakes etc..
It's a whole other discussion, but it's worth noting that bike design is more focused on aero / ride comfort these days, as the 6.8 kg UCI limit renders really light bikes pointless.
The real difference on the road for me is the weight distribution. An old school steel frame is not actually that heavy, but the forks are. Once the forks are made carbon, a whole load of weight disappears from the front. After 30 years of man-handling steel bikes up hills, the carbon bike has shown me that my technique is poor - I'm constantly pulling wheelies on steeper inclines, and actually flipped over backwards on a 20% grade!
One more thing - top line race bikes (still predominantly Campagnolo equipped) generally got heavier towards the end of the 80s/early 90s. For example Columbus SLX tubes are heavier than SL, and the new generation of Campagnolo components were heavier - particularly the chain sets and brakes (Delta, Dual Pivot). First there's the functional breakthrough, then it takes a while to match it with light weight.
I take it everyone's seen: