Does Outlaw recommending putting Spikes on subwoofers? What is the general feeling reguarding this for any subwoofers?

For what it's worth, Outlaw's LFM-1 and LFM-2 come with spikes and isolation discs (to save hardwood floors from being stabbed to death).

Gonk:
Noted.
But...is there an advantage to using the spikes if on a rug, instead of the discs?

With the LFM-1 and LFM-2, you really need to get the sub elevated enough to give the driver and ports room to breath. If you have deep carpet, I've even heard of folks putting a board under the unit to keep the carpet from interfering with the driver (although blocks under each foot would probably also work without being as noticeable).

In general terms (subs other than the Outlaw units), I don't think that Outlaw's ever stated a recommendation - can't think of a case when they would have needed to. If your sub was transmitting excessive vibrations to the floor, spikes might help. Of course, spikes might just channel the vibrations to smaller points on the floor (the energy's got to go somewhere, after all). Personally, I'd go with the manufacturer's provided feet for a sub unless I had a problem.

I have mine sitting on an auralex subdude in a carpeted room without the isolation discs.

platforms and spikes and isolation discs are not really necessary for sub performance. placement is the primary thing you can do to affect the performance of your sub. if your floor is unlevel, i would recommend putting your sub on a levling platform and thats about it.