I'd taken some unguided subs of m31 the other night and unfortunately most showed signs of star trail.
Rather than toss them, I processed all of them as usual.
The first photo is what I finished up with.
I then applied the "Star Rounder" plugin
(you'll find it here
http://www.tpo.ca/PS_Tricks/Various_...Techniques.htm )
and ended up with what you see in the second photo.
It's a quick fix.
Mind you, there is a trade off in the overall quality of the image. But I can live with that.
Image 23x2min @ ISO 1600
processed in CS3 and Paint Shop Pro
ED80, HEQ5Pro