I made the mistake of using it the first three weeks I had my pig, but as soon as I knew better for certain, I changed to aspen or kiln dried pine. Just recently I read somewhere a person say "the Phenol issue is just a bunch of garbage. I want to post a few links for newcomers to find this thread as a reference, that cedar is indeed bad for pets.
I want to add my personal opinion that liver toxicity can go undetected until the day a pet passes away. So how can these people say the pet lived just fine on cedar if they did not have an autopsy done to determine if there was liver damage. The pet can look just fine and the owner not realize a thing. Yet all the time he is suffering from pain and internal problems related to liver toxicity.
Also; I did an experiment long ago with my gerbils before I knew how bad pine and cedar are. The 55 gallon cage had three sections a gerbil could access, different bedding in each... pine, cedar, aspen. The gerbils, not knowing what was best for them, chose the room they liked best rather than which bedding was best for them. So the bedding was alternated from one room to the next at weekly intervals at cage cleaning time.
The results were that when the gerbils lived on pine or cedar they were very lethargic and did not eat as much. They did use their wheels, but compared to how often they used it when housed on aspen there was an amazing difference in activity level. With aspen they were very lively and almost hyperactive like a gerbil should be. After a time the gerbils did seem to learn what was good for them and spent more time in the aspen room than the others.
My conclusion was that the gerbils were lethargic on the pine and cedar due to the aromatic phenol oils. In fact, during the time I housed my Guinea pig on cedar I too felt the effects of lethargy. His cage was near my bed and I could not watch tv during that time without falling asleep. Things returned to normal when I switched his bedding.
I hope that people who are convinced cedar is fine will have a big enough heart and mind to consider the pets before their opinion and not take the chance of housing on cedar or non-kiln dried pine. If there is even the slightest chance that something is damging to them, that should be enough for someone who loves their pets to not take the risk.
Off my soapbox now and here are the links to references that tell of the damage of cedar and pine.
Some of them focus on gerbils or rats and mice, but I believe it applies to all small animals.
And two arguments supposedly for the opposite viewpoint, yet in at least one of them it states untreated softwood shavings are not recommended for pet use because it could affect an animals metabolism.