I will try retyping it slowly:
It seems to me that "a working USB 2.0 driver" means a driver "working" and "working at USB 2.0 speed".
In my perverted mind, if the BIOS USB 2.0 driver is working at 1.1 speed, then it is not working, but the number of such motherboards (having USB 2.0 capable chips BUT having a BIOS USB 1.1 speed driver are not that much common anymore).
Well my Asus EeePC 904HA BIOS can access files 100 times in a loop in 5 seconds, but with the grub4dos usb driver it does it in under 2 seconds.
100 loop ls /file test (BIOS times)
Asus EeePC = 5sec
Acer Aspire 7741G = 2sec
The EeePC also can boot from a USB HDD or Flash drive, but it cannot access sectors past 137GB (which is a very common bug with many BIOSes it seems). e.g. AWARD V6.00PG BIOS
In both cases the USB boot section of the EeePC BIOS could be described as 'working' as it does boot at a reasonable speed and does work - but it has bugs and is not particularly fast.
The very slow system that I mentioned was a reasonably modern system as it had USB 3 ports but seemed to have a problem with a particular make of USB Flash drive (which the grub4dos driver did not).
See posts by Jon and Neil on the E2B forum - http://www.easy2boot.com/forum/
Plop! is a read-only driver - it is not compatible with E2B or any grub4dos command that writes to the USB drive like default or dd or partnew.