Finally got a DVD+R DL burnt 
Last week I attempted to burn a ‘Traxdata’ DVD+R DL on an LG4120 using Firmware version A102 - it failed during lead in (creating a nice, expensive coaster!). Computer problems prevented me from doing anything else that weekend.
Last night I flashed the LG drive with the NOAD firmware following the instructions at:
http://www.cdrinfo.com/Sections/Reviews/Specific.aspx?ArticleId=9931&PageId=21
This unofficial firmware adds DVD-ROM Booktype and improves compatibility with various media types (an official LG firmware upgrade is due soon).
Having no more Traxdata media I used a (cheaper) Verbatim DVD+R DL 8.5GB disk for the project. Burner used was TMPG Encoder Author v1.6 Burning Tool. It worked flawlessly - it detected the disk, recognised burning speed of 2.4x and wrote the 7.8GB project (three episodes of a series recorded on a Panasonic HS2) to the disk in 43mins 40secs.
I’ve test compatibility with as many units as I can although it’s a totally random selection of my current/old DVD players, friends/nextdoor neighbours equipment and parents/nearby relatives
STANDALONES
Arcam DV88 Played no problems
JVC THRA75 Played no problems
JVC HVS30 Played no problems
Panasonic E55 Played no problems
Panasonic HS2 Played no problems
Philips DVDR1000 (original firmware) Played no problems
Sony GX3 Initially played but had problems on second layer
Toshiba 210 Failed to play the DVDR - disk error
Toshiba 330 Failed to play the DVDR - disk error
DVD-ROMS
Advent DVD-ROM (2002 series) Read no problems
Creative Labs 1998 Model Wouldn’t read/no disk access
Dell Inspiron 8100 Would not read
Dell Inspiron 8500 Read no problems
LG4040 Wouldn’t read/no access
Panasonic DF310 Read no problems
Samsung DVD-ROM Read no problems
Toshiba 1612 DVD-ROM Wouldn’t read/no disk access
All in all I think the compatibility is quite encouraging!