those of you with Simms jackets - if your getting wet sleeves under your coat then your not tightening the wrist enough. it should be fairly snug but not so much so your hand goes tingly. I have done as Matt and reached all the way down and left my arm in the water until i could feel the water getting by the cuff, took probably close to 20-30seconds with my G4 jacket
now if im fly fishing a single hander i do get damp to my elbow from the slight amount of rain trickling down my arm all day while casting. with my old raincoat i would have a puddle at my elbow. I have owned so many different coats/jackets/cheap wading jackets and glad i finally broke down and got something worth what i spent (im not however looking forward to the day i ever have to replace it)
Biggest reason for a wading jacket and especially one worth something is the breathing ability, this will keep you dry, warm and very comfy. remember that wading jackets are just shells for the most part and its up to you to layer properly underneath. I have been out in -12 weather in a t-shirt, Airwalk sweater(cotton) and then my wading jacket and been perfect, when i start walking alot of times i actually have to undo the jacket because i start getting to warm and sweating is bad in cold weather. another huge thing that some wading jackets dont have is handwarmer pockets, I will never have a jacket without them and they need to be fleece lined, i actually keep my fingertipless gloves in there full time.
for those of you that are shopping around for a jacket, make sure you do your research because you can get pretty good quality for half of what the Simms jackets cost. my dad himself wears a jacket from Vision and he loves it, i grabbed it used for him for $120 i think its normally around $200 so it can pay to look around especially if you can find stuff on sale, I know of a website thats blowing out alot of LOOP stuff but they arent a supporter here so ...........