My recumbents varied in weight from about 22 lbs for the M5 to about 32 lbs for my M1 low racer. On flat terrain (hard to find anything else in Florida), I don't notice the difference when riding them. On uprights, it's a different story. I can definitely feel the difference between my 2012 14.8 lb S-Works Venge and some of the newest offerings from Trek which weigh several pounds more. The newer bikes just felt sluggish off the line and when making rapid directional changes. I was also completely underwhelmed when comparing Specialized's newest Roubaix to my 2013 model. At 16 lbs, my Roubaix isn't the lightest upright I've ever owned, but the newest model feels even heavier. Strangely, the Roubaix's ability to absorb bumps hasn't improved at all; in fact the newer one felt harsher on brick roads than my old one.
Having had disk brakes on all my mountain bikes, I'm certainly aware of their superior braking abilities in inclement weather and better modulation in all conditions, but for me the difference isn't enough to consider upgrading. One thing that also needs to be said is that there's a marked difference in performance among rim brakes. The ones on my Vendetta are fantastic, the ones on my M5 are marginal, and the ones on my M1 are terrible. I'd love to know what makes the ones on the Vendetta so good. They've given me stellar braking performance no matter which wheels I've used, and I've already changed the brake pads once, so the difference is definitely in the brakes themselves.