Guys, I'd appreciate if you give me a pointer and answer my previos question - I cannot afford to perform lengthy experiments on this system.

Meanwhile I've upgraded to 3.0.0-16 and it changed things a bit once more: booting in safe mode doesn't guarantee success any longer (on maybe I was just lucky previous times), but it allowed some insight into what's going on: when my system lockes up the last line on the screen is always a DVD drive detection (3 out of 3).

[    3.116027]  sdc: sdc1                                                                                              
[    3.116230] sd 2:0:0:0: [sdc] Attached SCSI disk                                                                    
[    3.117191]  sdd: sdd1                                                                                              
[    3.117422] sd 3:0:0:0: [sdd] Attached SCSI disk                                                                    
[    3.120788]  sdb: sdb1                                                                                              
[    3.121017] sd 1:0:0:0: [sdb] Attached SCSI disk                                                                    
[    3.130707]  sda: sda1 sda2 sda3                                                                                    
[    3.130990] sd 0:0:0:0: [sda] Attached SCSI disk                                                                    
[    3.192021] usb 3-3: new high speed USB device number 2 using ehci_hcd                                              
[    3.278654] scsi 5:0:0:0: Direct-Access     ATA      Hitachi HDS72202 JKAO PQ: 0 ANSI: 5                            
[    3.278803] sd 5:0:0:0: [sde] 3907029168 512-byte logical blocks: (2.00 TB/1.81 TiB)                                
[    3.278810] sd 5:0:0:0: Attached scsi generic sg4 type 0                                                            
[    3.278878] scsi 5:0:1:0: Direct-Access     ATA      Hitachi HDS72202 JKAO PQ: 0 ANSI: 5                            
[    3.278949] sd 5:0:1:0: Attached scsi generic sg5 type 0                                                            
[    3.278966] sd 5:0:1:0: [sdf] 3907029168 512-byte logical blocks: (2.00 TB/1.81 TiB)                                
[    3.278997] sd 5:0:1:0: [sdf] Write Protect is off                                                                  
[    3.278999] sd 5:0:1:0: [sdf] Mode Sense: 00 3a 00 00                                                               
[    3.279010] sd 5:0:1:0: [sdf] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA                 
[    3.279583] scsi 8:0:1:0: CD-ROM            TSSTcorp CDDVDW SH-S202H  SB00 PQ: 0 ANSI: 5                            

>when it locks up it is always here

[    3.281276]  sdf: sdf1                                                                                              
[    3.281336] sd 5:0:0:0: [sde] Write Protect is off                                                                  
[    3.281389] sd 5:0:0:0: [sde] Mode Sense: 00 3a 00 00                                                               
[    3.281416] sd 5:0:0:0: [sde] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA                 
[    3.281510] sd 5:0:1:0: [sdf] Attached SCSI disk                                                                    
[    3.281907] sr0: scsi3-mmc drive: 48x/48x writer dvd-ram cd/rw xa/form2 cdda tray                                   
[    3.281969] cdrom: Uniform CD-ROM driver Revision: 3.20                                                             
[    3.282071] sr 8:0:1:0: Attached scsi CD-ROM sr0                                                                    
[    3.282109] sr 8:0:1:0: Attached scsi generic sg6 type 5                                                            
[    3.289956]  sde: sde1                                                                                              
[    3.290188] sd 5:0:0:0: [sde] Attached SCSI disk                                                                    
[    3.348774] usbcore: registered new interface driver uas                                                            
[    3.436586] Initializing USB Mass Storage driver...                                                                 
[    3.436713] scsi10 : usb-storage 3-3:1.0                                                                            
[    3.436973] usbcore: registered new interface driver usb-storage                                                    

Note that DVD is attached to IDE, not to SATA (primary master, the only device)