Though I'll politely disagree on whether Sony cameras are stacking up well to any other brand (I personally find Canon/Nikon/Sony/Panasonic/Fuji all basically on the same level of quality, build, and capability, with Kodak, Pentax and Olympus fine choices as well)...I will agree somewhat with the recommendation to not base your decision on your memory cards.
In fact, if your Sony takes the Memory Stick cards, rather than the Memory Stick Duo cards, you're out of luck with using the cards in any of Sony's new cameras. Sony's Duo Memorysticks are about 1/2 the size of the regular ones, and most of their new cameras take those smaller cards only.
One other side-point - re taking night shots or moving pictures without blurriness - the camera is actually rarely ever the problem here. There really is no brand of P&S camera you can buy which will be able to take handheld snapshots at night without blur - it's simply beyond the capabilities of small sensor compact cameras. The closest any have ever come was Fuji's F20/30...but they've since been replaced by newer models that don't perform as well as the older ones.
Really, a little basic photography lesson would help a great deal - even with a 6-year-old compact 3MP el-cheapo cam, you can take a lovely night shot if you follow some basic rules (place the camera on a level surface or tripod, and use the self timer to snap the shot). And for action or moving shots, the same holds true for a $5,000 DSLR camera setup as for a $100 Kodak P&S - light, light, light! The more light the camera has, the more it can stop the motion. Bright afternoon daylight is best.
DSLRs with big sensors and interchangeable lenses can compensate for less light by shooting cleanly at much higher ISO sensitivity than typical P&S cameras, and by using specialized low light lenses designed to admit as much light through the aperture as possible.
If you just want to upgrade your camera to something that is of decent quality, reliable, takes good photographs, is compact, etc - then check out Sony's W300 or other W-series cameras, Canon's SD1100 or other SD-series cameras, or Panasonic's LZ or TZ-series cameras. Most get very good ratings, have respectable image quality and lots of user-controllability, and are all manufacturers with good reputations and build quality. You'll likely be in the $200-300 area for a decent P&S compact in any of these ranges.
But you should try a few techniques with your current camera to improve your photography skills - you might be surprised at what you can accomplish with an older 4MP camera, and find it still can meet all your needs (unless you need to do any shooting for
National Geographic anytime soon!).
