I have both my PS3s on their own shelf without any other equipment or obstructions around them. IN fact, the only additional thing I could do is stand them vertically maybe, but they are ugly enough sitting flat.
Keep in mind, some people have a LOT better hearing than others. I personally have been an audio engineer for the last 11 years. I wear specially molded earplugs at the movies, hockey games, and even when vacuuming. These things along with concerts, loud HT systems, lawnmowers, etc. all destroy your hearing permanently. Most people never notice what they are missing.
I fought with a hotel manager after they put me in three rooms in a row with squeeling TV sets (my wife insisted on watching). They had sets that were PAL or NTSC and they all has horrible flyback transformer ringing. It was like someone blowing a dog whistle in my ear. The hotel manager insisted that I was crazy since he heard no such noise whatsoever. I guess his hearing cut off before 15.6 kHz.
We ended up watching the slingbox on our laptop instead of me suffering through the shoddy TVs. To this day I am sure that hotel manager thinks I was nuts.
Bottom line, the PS3 fan noise is objectionable in a quiet room. Tile and reflective surfaces will only make it worse. My best friend doesn't hear my PS3 when a BD is playing, but I certainly do. And for those that think the answer is to "turn it up!" keep in mind what I said above. The more you do this, the more PERMANENT hearing loss you will incurr.
They say that hearing is the first to go...it's no wonder why!