Weak mags springs would also cause a failure to eject. There are many causes. If you are going to get any work done on your gun (feed ramp polishing, ejection port work etc) I would highly recommend Mike LaRocca in Worcester. Mike is an excellent gunsmith.
Slam Fires =
Here are a couple of my favorite sites:
http://thefiringline.com/forums/index.php?
http://forum.m1911.org/
The second one has Brand specific forums....