I have a SE 380 explorer. The drop stitch makes for a very stable boat...as in I often stand and flycast in moving water (the same with NRS Pikes- the only two IK's I've paddled w/dropstitch). The flat bottom also means they don't track the greatest without a skeg.
It also makes for an awesome gear hauler (for the SE anyway)...I can pack me, my girlfriend and campgear for a few days in one.
I often run class 3 in it...the drop stitch makes it handle much like a raft, still very stable, but the flat floor can make them a little sticky in holes (which can be fun to surf with!) or you will occaissionally get typewritered. It's not the best whitewater craft but I have total confidence in the boat and can make it do what I need it to do and I'll usually run whitewater without the skeg on. It is a great fishing or camping IK.
The "regular" floor you are speaking of (basically the one big bladder in the shape of a cat tube kinda) makes for a more nimble boat, easier to "carve" and use your hips to shift weight and get on edge...but this also means less stability. I won't be flyfishing standing on one. They do track better than a dropstitch IK does. But because of this they are also pushier in a way when perpendicular to stream flow as the tube "bulge" along the bottom creates a skeg of sorts and catches current.
Sometimes you'll find the current just kind of slips on under the IK with a dropstitch floor (which helps seeting up drifts for fishing). If you find the right currents you can even kind of surf in place with no real discernable/surfable features that one would normally recognize as such.
Bottom line the dropstich is great for gear and stability (therefore fishing and camping) and I find it more comfortable. The bladder floors provide a sportier, straighter tracking ride. I keep telling myself I'll get a more "sportier" for just purely whitewater/fun runs, but I have more use for fishing/camping IKs....even when I do buy one for myself, I'll never give up the SE.