1. If most/all of your images will end up on the web (e.g. you don't plan to print lots of large images for wall-hanging and gallery display), then the quality of a DSLR is really a non-issue. The quality of superzooms is MORE than enough for excellent 800x600 images online. But if you *do* plan to be printing a lot of large images (bigger than 8x10") then you'll need the superior resolution and quality of a DSLR.
2. If compactness/portability is important... and you don't want the hassle of switching lenses, then the superzoom is definitely the way to go. Some have commented that superzooms like the Canon SX10 are almost as big as a DSLR...but they're still *not* as big (especially when you add a long-range zoom to the DSLR).
3. Superzooms give you virtually all of the manual control of aperture, shutter, and focus that DSLRs offer. They also offer advanced features like exposure and focus bracketing, and even white balance bracketing (on some models).
4. Depth-of-field control is somewhat more limited with a superzoom, but this primarily applies to shorter focal lengths. The great thing about superzooms is focusing at 20x zoom on an object just 10 feet away...which gives you amazingly narrow DoF for some beautiful results.
5. Superzooms shoot video; most (if not all?) DSLRs don't. If you ever want to shoot some video, this is a consideration.
6. RAW format images: most superzooms won't shoot RAW (the Canon SX10 doesn't, but I think the Panasonic does?). For me, this isn't really an issue, because almost all of my shots end up on the web (see #1 above).
7. Low light - no question, DSLRs perform better here with less noise. But I've found my superzoom (with image stabilization) does perfectly well when (again) the final result is destined for the web.
The bottom line is that if you are NOT a working, professional photographer, there's a LOT to be said for going with a superzoom.
In my opinion, (and I'm not a working professional photographer), the gains achieved by going with a DSLR are simply not significant enough to warrant the increased price and reduced compactness.
For their price and their relative compactness compared to a DSLR, superzooms are a fantastic deal with enormous range and flexibility.
The most important thing is to know what you want from your camera, what it can do and set appropriate expectations on it. You might be pleasantly surprised when it delivers more when least expected.
