Hey Atlas,
Wow.. speccy lightning shot! well done!
Its been threatening a storm here in Perth for the last day or two, but it never eventuated (and I think its supposed to be sunny again tomorrow).
With regard to your blurry shots, I suspect it is due to camera-shake. The longer the focal length you use, the more the shake will be exaggerated and so the faster your shutter speed needs to be to avoid noticable blur. Check your EXIF metadata to see what your shutter speeds were for these shots. Try using Shutter Speed Priority (Tv mode) and setting the shutter speed manually based on the info below.
There is a very general rule of thumb that says in order to get sharp hand-held shots, you need a shutter speed that is at least as fast as the reciprocal of the focal length (when converted to 35mm equiv.) This means that if you are shooting at 100mm (which is 200mm when converted to a 35mm equiv) then you need a shutter speed of 1/200th of a second in order to keep it sharp. When you are shooting at 50mm (100mm equiv) then you can get away with a 1/100th sec shutter speed, and so on.
In reality, everyone is different, and there are many factors that can influence how steady you hold a camera... so you'll need to adjust this rule to suit yourself and the conditions. But it gives you a good starting point and describes the relationship between shutter speed and camera-shake nice and simply (ie if you double the focal-length, you'll double the camera-shake and require a shutter speed twice as fast to compensate).
Oh, and using a flash is also great for keeping shots sharp, Not only does the extra light mean you won't need as fast a shutter speed, but also because the flash is so brief, even when using it with a slowish shutter speed it can have a good sharpening effect. Its just a shame the internal flash gives such a harsh look on most shots
Here is another thread with lots of good advice for getting sharp photos:
http://www.shuttertalk.com/forums/viewtopic.php?id=4145
Regarding the filters, you should have no problem using a UV filter at night except perhaps sometimes it might show a bit more flare from bright lights, but it shouldn't require longer exposures or reduce the amount of light entering the camera like a polariser will. Many people keep UV filters fitted to the front of their lenses permanently for protection which is quite sensible (but personally I prefer lens hoods for protection instead).
I have used stacked filters numerous times, but be aware that this can cause vignetting, especially with wide-angle lenses or when using more than 2 filters. Also every extra layer of glass you place in front of the lens will decrease optical quality slightly, introduce another two dust-gathering surfaces, decrease contrast slightly, and increase the potential for flare. But while this sounds bad, these effects are
very minor and there are plenty of more important things that make or break a shot...
Purists may prefer not to use filters unless necessary, but for the vast majority there will be no noticable difference.
Cheers
Adrian