Hi All,
One nice way to create star-trails is to take several short exposures and then merge them together.
Using an interval remote you can take several short exposures and not risk a problem if a car, an airplane or a crazy guy with a flashlight come across your shot.
I use startrails.exe from this site as manyof you know:
http://www.startrails.de/
What is probably new and I'd like to present here is Star Tracer a nice new app by Max Lyons that can fill the gaps between several short exposures enhancing a star trails shot.
http://www.tawbaware.com/startracer.htm
It can also enlarge trails, it's up to you if that's cheating or not and how much you cheat
I hope you find this app useful if you like doing star-trails!
Experimentally it can also un-trail some images if you create a rotation and then substract the images but I haven't toyed with that yet.
Luis