Very useful (I love hifishark). I am happily exploring The Daily Audiophile.
Two sites I Like
A quick place to go to see what new reviews are out there; The Daily Audiophile
Fastest way I know to check the used market; Hifishark.com
Both are aggregators of info from other sites, meaning that Hifishark includes listing on Audiogon but other sites as well. Same goes for The Daily Audiophile.
Hope you find this useful.