If you want to be creative with long exposures I suggest you invest in a Hoya Infrared filter (R72).
To respond to my own suggestion. I borrowed a Hoya Infrared filter (R72) to get a specific effect I wanted with my 5N. It worked really well and I was pleased.
When I tried to make more conventional IR images I was less happy with the result. To quote jhoughton on this thread:
what I didn't expect was that I got no discernible IR effect on grass or foliage. I guess that the IR blocking filter on the sensor is fairly strong and what I'm seeing is due mainly to the small amount of light from the longer end of the spectrum getting through the 720 filter. I've subsequently had the camera converted (720nm) and I'm very happy with the results.
So you can get some interesting effects with the Hoya, but it seems it is just restricting light to the longer end of the visible spectrum and not really IR. Sorry for any confusion caused.