I bought a 2008 Nevada (2) weeks ago and am still learning to ride. This is my first bike, I'm 49 years old, 5'10", 205Lbs and just fit nicely on this bike, however, good luck if you're any bigger, as I really do just fit.
I find this bike is very easy to ride. For example, as I stated this is my first bike, and I bought it on a Thursday and passed my New York State road test on the following Tuesday. I attribute this to the great balance / handling / maneuverability and perfectly set idle of this bike.
Regarding the perfectly set idle, (I was able to perform on the road test (2) right hand circles & without stopping (2) left hand circles and then without stopping (2) figure eights all without applying throttle or brake!)
I am getting 55 MPG on my all rural commute, twisties, hills at about 60 MPH.
The longest I've sat in the saddle is about (2) hours, and while I wasn't sore or in discomfort, I was ready to get off. However after a short rest, I'm always eager to get back on. Do note I'm a new rider and am still breaking it in, mine hasn't seen 5k on the tach yet, so not sure if it's underpowered or under ridden.
Bottom Line: I love it, Nobody's heard of Guzzi, but everybody wants one!
I have just completed a 3200+ mile trip (now 7500 miles on it) on my 2007 MG Nevada 750. It fits and rides like a charm. I am 5'8" 165 lbs with a lot of previous motorcycle experience, but just started riding again after a 25 year hiatus. If you want to read details about the trip or the bike performance and statistics, see wildguzzi.com forum discussion article "Trail of a New Guzzi Nevada 750 Driver". I think it will answer all of your questions.