Thanks for the great tutorial, I followed it step by step. I use Verbatim dl's and this is the output in the terminal :
Executing 'builtin_dd if=/Users/idog/trlegend.iso of=/dev/rdisk5 obs=32k seek=0'
/dev/rdisk5: splitting layers at 1848848 blocks
/dev/rdisk5: "Current Write Speed" is 2.5x1352KBps.
4947968/7572881408 ( 0.1%) @0.7x, remaining 101:58 RBU 100.0% UBU 2.0%
14909440/7572881408 ( 0.2%) @2.2x, remaining 59:08 RBU 100.0% UBU 55.1%
26214400/7572881408 ( 0.3%) @2.4x, remaining 52:46 RBU 100.0% UBU 75.5%
3770580992/7572881408 (49.8%) @2.2x, remaining 19:26 RBU 100.0% UBU 98.0%
3782311936/7572881408 (49.9%) @2.5x, remaining 19:23 RBU 100.0% UBU 63.3%
3787653120/7572881408 (50.0%) @1.2x, remaining 19:23 RBU 100.0% UBU 73.5%
speed drops, like you said, probably the layerbreak
3787653120/7572881408 (50.0%) @0.0x, remaining 19:26 RBU 100.0% UBU 100.0%
3787653120/7572881408 (50.0%) @0.0x, remaining 19:30 RBU 100.0% UBU 100.0%
3787653120/7572881408 (50.0%) @0.0x, remaining 19:33 RBU 100.0% UBU 100.0%
3787653120/7572881408 (50.0%) @0.0x, remaining 19:36 RBU 100.0% UBU 100.0%
3795582976/7572881408 (50.1%) @1.7x, remaining 19:35 RBU 100.0% UBU 57.1%
3806232576/7572881408 (50.3%) @2.3x, remaining 19:31 RBU 100.0% UBU 59.2%
3817930752/7572881408 (50.4%) @2.5x, remaining 19:27 RBU 100.0% UBU 65.3%
3828416512/7572881408 (50.6%) @2.3x, remaining 19:24 RBU 100.0% UBU 75.5%
second layer started
7550795776/7572881408 (99.7%) @2.5x, remaining 0:06 RBU 65.8% UBU 59.2%
7561543680/7572881408 (99.9%) @2.3x, remaining 0:03 RBU 33.8% UBU 67.3%
7572848640/7572881408 (100.0%) @2.4x, remaining 0:00 RBU 0.1% UBU 69.4%
builtin_dd: 3697696*2KB out @ average 2.4x1352KBps
/dev/rdisk5: flushing cache
/dev/rdisk5: closing track
/dev/rdisk5: closing disc
Everything peachy, you'd think. I pop it into my 360 and it gives me an Unrecognized Disc error

I'm using an external Pioneer DVR-111D, fw 1.23. My system is an iMac 20" Intel Core Duo 2.0 ghz with 2GB Ram. OS X 10.4.7, single partition.
When I use this drive on an XP Laptop and use CloneCD I can burn backups without problems (using the same verbatim disks), not a single coaster to date..
Anyone got a clue to why it doesn't work (to be sure it's not the imagefile which is faulty, I've written the same iso (of course in conjuction with the .dvd file) on the XP Laptop with CloneCD and it worked like a charm..)
It's possible your drive isn't bitsetting the burn to DVD-Rom and that your 360's formware doesn't ignore the bitsetting....
You can try to use dvd+rw-booktype, but I haven't found out a way to make it work in OS X yet (mainly because you only get a logical device in OS X from a removable drive with media present... and you need the drive empty to do a bitsetting change). You can likely permanently change it in windows and not have to worry about it though...
In addition to my internal burner, I have an NEC 3540A in an external firewire/usb2 case... Just used it with growisofs to burn at 8x
The one nice thing about the NEC.. is that there are OS X flashing utilities for it (binflash