This is an interesting topic, and it's also interesting that O2 has been mentioned here. I switched to pure O2 last year for a couple of reasons:
1) Ease of use - I was tired of waiting 20 minutes with an aquarium pump. I was definitely tired of shaking, and I didn't feel like dealing with other apparatuses.
2) Oxygenating lagers - I wanted to get above 8ppm, which was claimed to be the upper limit using air.
So, is my beer better? I can't tell. The point was to maintain ales exactly as they were before, since over-oxygenation could change the character of estery beers like Belgians. I haven't noticed a difference in the ales, but I also can't say that lagers are any better. But it's sure easier and faster than an aquarium pump.
I think my biggest change in the past year was focusing on keeping pH down even lower than before - mash pH of 5.4 or so for lagers, and 5.5 for ales.This means phorphoric acid in all strike water, lactic acid or acid malt in light lagers, and almost never using chalk since I rarely see a mash pH of a dark beer get lower than 5.4. I even acidified the wort in the kettle for my last pilsner to 5.35 with more lactic acid. This has definitely had a positive effect on my beer.