I just bought my first nebula filter for my 8" Dob last week on a trip to Melbourne, an Astronomics UHC-E filter.
I tried it for the first time on the Eta Carina nebula and Orion nebula's on Thursday night, wow
Even though I was only using a cheap GSO/Bintel 15mm wide view eyepiece and both nebula's were fairly low in the sky with hazy clouds about the filter made a HUGE difference.
I tried it both with and without the filter, and the subtle detail I could pick up was hugely improved with the filter, almost giving the nebula a 3 dimensional shape. I compared what I could see of eta carina with photo's afterwards, and although I obviusly couldn't see colour I could see a much bigger extent of it, subtle mottling and hugely improved contrast between the dark rifts and nebulosity.
The orion nebula was low down and covered with hazy cloud to the point that I could only just make it out with the naked eye but through the filter I could a huge extent of its "wings" with a subtle green colour.
Overall I'm really happy with it and am looking forwards to a hopefully clear dark night tonight.
Kind regards
Ant