When I switch from regular 26 x 2 all-purpose tires and tubes to my Pasela 1.25's with the ultralight tubes, the bike takes off like a rocket from a stoplight. I'd have no problem identifying the two configurations in blind testing, that's for sure. The weight difference is about... lessee here... 1100 grams or so. The cost difference is reasonable.

For me as an arterial commuter, getting up to cruising speed quickly is definitely useful. Surging from cruise to ~30mph is also useful at times. I don't always use the Paselas, but when I do, there's no mistaking the change in acceleration.