As told, I tested it w/o nvidia module loaded, here's what I found:
1. It now doesn't hang on scanning for devices.
2. It now hangs on acquiring preview, logs will follow.
...
Apr 3 15:54:27 techno kernel: Unable to handle kernel NULL pointer
dereference at virtual address 0000014c
Apr 3 15:54:27 techno kernel: printing eip:
Apr 3 15:54:27 techno kernel: c03d8143
Apr 3 15:54:27 techno kernel: *pde = 00000000
Apr 3 15:54:27 techno kernel: Oops: 0000 [#1]
Apr 3 15:54:27 techno kernel: PREEMPT
Apr 3 15:54:27 techno kernel: Modules linked in: nvidia
...
Still with nvidia.Em, there's also the same (w/o oops) with out that module, each of that situations was separated by a reset. It was working well in 2.4.x so I guess it'a a problem with the card's (00:0c.0 SCSI storage controller: DTC Technology Corp. Domex 536) driver.
An Oops with the nvidia module loaded since the last boot is simply not debuggable for anyone except nvidia.