I'll do this kind of out of order, I'm pretty tired but I know a lot of people wanted info....so here it is.
Merch was fuckin expensive for Slayer, Mayhemfest and all the headliners etc. (like 30-35$ for a T shirt.)
I got a Cannibal shirt, they have all the shirts on their webstore plus an Evisceration Plague tour shirt, all are 21$. The comic/CD is 20$ and comes with a wristband so you can get priority in meeting the band. I don't know about any of the other bands.
There was initially a very long line, but these best buy people gave me and my friends free "vip" passes for singing up for their rewards program (which was totally worth it because we got in with a 10 person line in about 5 minutes)
Went straight to the Cannibal booth and got an Eaten Back to Life shirt, then the Hot Topic and got the comic. Drank some rockstar, then went to meet Cannibal. That was awesome, but I guess they switched Behemoth to earlier in the day, which sucked because they were one of the reasons I went. Missed half their set. Nergal wears a new mask and the bass player spits blood, no bible tearing. They are always great though.
I didn't really pay attention to many of the other bands, but I sat through BDM and JFAC in the front so I could get a front spot for Cannibal. Cannibal were amazing, but they had a pretty short set. I think the crowd got mor e into them then anyone else.
The rest of the time between CC and Slayer was spent just goin around and talking to people.
Slayer were pretty good. I don't love them, and it was sad that they didn't play anything of SNM. Oh well. They have a lot of energy and everyone loved them. They had lots of fire and "evil" looking things (pentagrams etc), but it didn't really work and looked kinda cheesy. But maybe that's the point.
I made it about half way through Manson's set and gave up, I don't care at all about him.
That was brief,but I'm tired. If you've got specific questions about anything I'll see if I can remember.