So this may be out of context and I apologize if it is - here is the info on my banned box (as I have two) - 1 modded - one not. Of course the not modded box is not banned.
- Banned? Yes
- Spring update? Yes
- Drive brand and model: Samsung MS25
- Current firmware: ixtreme 1.0
- Previous firmwares: NME 1.2
- Games with achievements listed on your xbox.com: ? Yes
- Update to the new jitter fix FW before or after Spring update? N/A NME 1.2
- Last date backup was played: 4 days after spring update
- Country: USA
A couple of thoughts:
1) I was using the NME 1.2 - without the network disconnect option. I had played non stealth patched backups. I updated anytime Xbox Live said there was an update. Obviously - the NME 1.2's firmware is not exempt. This leads to two points of interest there:
a) All of these folks are talking about using a brand new xbox with the iXtreme firmware. Cool - however, how do we know if MS is taking the initial snapshot prior to shipping the xbox's to their retailers? So new box or not - they could shut that down as well. I know, sorry - another "what if"

NME backups are patched with the NME associator. Quit possible - even if a backup is stealth patched - the the NME Associator - which relocates the Security Sectors - has been detected.
My best assumptions - stay away from the NME 1.2 etc unless you are using the network disconnect option.
Sounds like the ban checks (from most of the data I've looked at) are as follows:
Technicals - drive speed - seek time - lock on etc.
Log files of your xbox 360 (Logging all changes to hardware)
Non Stealth Backups.
Looks like we're all making some headway here. Good. Good.
Sncboom2k