I find it interesting that they reccomend oil change every 1 year/25,000 miles and a filter change every 6 months/12,500 miles. Seems that would be pretty cheap.
Also, I've got an old GMHTP around here somewhere, in it they ran some dyno tests on oil. Turns out changing from dirty conventional to new conventional was worth more hp than the change to synthetic. I think the change to syntheic was worth maybe 1-2hp on a 400+hp LT1. Thats somewhere about the limit of accuracy of the dyno they were using.
I still use mobil1 in everything I've got. I havn't found a reason to switch to AMSoil yet, though I've considered trying it.