Most of my jerseys have elastic waists. I've never noticed an issue with it compared to my non-elastic jersey...in fact I had to go look to see if I even had one that wasn't elastic (and I don't have the most toned stomach in the world to say the least). The jerseys stay put right at the point of my hips, which is where they are cut to stay, even with my large hips without problems and don't cut into me (which I think would be my only complaint should it occur).

I've tried on a jersey with the arm elastic before and really didn't care for the restrictive sensation in that particular jersey. Could have just been that brand though.

Really it comes down to personal preference. I ride with a lot of racers, so "the look" is the tight club/race cut jerseys with the elastic rather than the looser fit type jerseys. I guess I've just grown accustomed to the more fitted feel and look. Some of my jerseys are cut well and figure flattering despite this, some probably aren't the most flattering things off the bike, but on the bike the only things people are seeing are my back and rear-end anyway.