Did my five year refresh on my gaming rig a while ago - switching from AMD Phenom II to a 5830k. In both cases I was using Asus Sabertooth, 990FXR2.0 in the old system, X99 in the new.
But I've noticed something slightly strange about the new setup. I'll press the power button and hear fans etc start for less than a second, (basically as if I'd just pinged the power button), then they spin down. There's a short delay (1-2 seconds) then they spin up again, stay running and the system goes through the boot sequence etc.
It's not a fault as such, because in every other* way the new setup is working fine, but it's just a bit strange - almost as if there's some capacitor etc on the new board that has to be fully charged before the system is allowed to start. PSU, case, graphics card and most of the storage was carried across from the old system, so I'm happy that any "problem" is not with them.
(* only other wierdness is that connecting the Akasa USB3.0 card-reader/front panel's Molex causes the optical drive - which is a SATA connection to not power up. Even if the two are on different cables).