To me the very biggest and singular outstanding difference is noise and resolving powers. And this boils down to basically an extra photoshop step or two. The biggest differences are really noticeable in CMOS vrs. Small CCDs - From bigger CCDs to smaller CCDs there's a difference too but it's not nearly as great (mostly it's just better in-camera NR vrs. having to do it in PS).
Anyway, as I see it it's like:
- CMOS: bring it in through CameraRAW color balance it, maybe do a little sharpening, maybe some Brightness/Contrast, scale for output, and your done.
- Small CCD: Color Balance in CameraRAW, do Levels, do Brightness/Contrast, do a USM at 50 pixels 20%, Do another USM at 1 pixel at a high percentage, increase saturation, noise removal, scale for output, another sharpen at less than 1 pixel and a lower percentage, and you're done.
So that's like 4 or 5 steps vrs. 8 to 10 steps for each image. And to me this is what the differences between a dSLR and a bridge camera boils down to. Having a nice app like Capture One (best semi-auto processor!!!) removes most of the differences but if you're fine tuning everything in Photoshop by hand it can be rather significant.
The sensor's resolving powers are noticeable and unresolvable (through software) only in some special circumstances. Astrophotography being one of them. Ultra sharp and fine fur in animal photography being another one. For example in this bridge camera shot:
It looks pretty good right? Nice and sharp, well defined, etc. But if you were to put a nice CMOS image (with a nice sharp lens [+$500 or more]) of exactly the same shot next to it for a side-by-side comparison you would notice missing detail in the tail feathers, wings, shoulders and head. More definition in the feet and toes. And the DOF would be slightly more dramatic as well. Almost no normal human can notice these things unless doing a side-by-side or trained and intent on looking for such things. Or at least I think so.
So to me it's a trade off of a little quality and a few extra steps in Photoshop for the convenience of having a rich feature set that is often better than even the most expensive dSLRs. I've had both - my last dSLR was the D2x. I usually change entire systems at a time. When I sell a system I usually sell all the lenses and everything and then rebuild. I'm really between dSLRs right now and this bridge camera is one that's left from a set I got for a job I did about 4 years ago. So I'm using it while I figure out what I want. I know whatever I get I'm probably going to get that casio with it.
I'll probably end up with a D700 but if Nikon comes out with a video capable dSLR I wanna see the specs on it first. Rumors are already circulating so I guess it will be pretty soon now. I probably sold my D2x too soon. I didn't know there was a full-frame semi-pro Nikon out or coming out, and had planned on getting the FF Canon. Now that it is out (The D700) I wanna wait still a little longer.
If you had a few thousand to spend there would be no question about it IMO tho. dSLR!
I would be taking photos of small insects especially and normal pictures such as animals and wildlife plants, and other common scenes such a sunset, beach, storms. 
Even with a lens that isn't capable of marco at all you can just screw on a high quality close-up lens (~$40) and get awesome bug shots. Most bridge cameras also come with very good macro ratios. The P&S cameras can get close but THAT close is NOT good for insect photography. Try getting 1cm away from a beetle or fly and you'll see what I mean - and you NEED to get "that close" with a P&S usually to get enough detail. You want a working distance of around 10" to 20" or so and still have the magnification power to bring it up close. This is available in bridge cameras, a dSLR macro lens. or a lens with a close-up attachment attached - but usually not a P&S.
