I play in my club's thirds team and I've only ever played one game in two years with an allocated umpire (only the firsts and seconds are guaranteed an umpire). Generally when I'm umpiring I give the bowler one loose delivery per over, either down leg or outside off. If it's obviously a wide then I call them, but line-ball decisions I ususally say to them on their way back to their mark "you can have that one mate, but next time it's wide". I notice most players really appreciate that (never seems to get reciprocated though!) and I think it's just a sensible way to go about it at our level.
The one time we did play with an umpire he called me the three times down leg side. On two of them the batsman stepped across his stumps and the ball only just missed leg. On the second one I cheekily said to the umpire "that's a bit harsh, I've nearly bowled him". No malice or anger, just trying to have a joke with him. To my shock the umpire snapped back "f-ck off, you keep bowling them down there I'll keep f-cking calling them, for f-ck's sake". I didn't take kindly to being sworn at and a few verbals ensued, to which I said "you're being paid to be here and you're swearing at players? That's not very professional." He said "neither is your bowling", to which I replied "well there's a reason I play in the f-cking thirds and not for Australia... there's probably a reason you're umpiring down here too, you useless b-stard."
The moral? I prefer to play without an umpire, thanks