What's the story with Amsoil?

Same here. Mobil-1 and a Fram filter (I like Fram!) ever 5K on the 4Runner and WRX.

That's where it came from.

Well - Amsoil has always been flaky when it comes to getting certified via the API's EOLCS system (the API "donut"). Only their XL-7500 series goes through the certification process. There have been rumors that Amsoil doesn't meet all API specs. It's not that it doesn't protect engines, but there have been allegations that their products have a boosted ZDDP level, which may foul catalytic converters.

From what I can tell, the actual product is fine. However - some are turned off by the often pushy Amsoil salesdroids who rave about the stuff all over the auto NGs. Red Line is another niche maker of lubes. They have a loyal following, but few people get upset at the mention as with Amsoil. They only sell through regular dealers (I've even seen some of their stuff at Pep Boys).