With a fresh install from Fedora-15-x86_64-Live-KDE.iso live usb creator works fine with or without persistent, any usb drive I have using the aforementioned iso as a source. However after updating the installation and using the same iso with any drive I have, it results in:

Fedora-15-x86_64-Live-KDE.iso selected
Verifying filesystem...
Verifying ISO MD5 checksum
ISO MD5 checksum passed
Extracting live image to USB device...
Wrote to device at 25 MB/sec
Setting up OLPC boot file...
Installing bootloader...
Invalid flag provided.
LiveUSB creation failed!
Invalid flag provided.

livecd-iso-to-disk works, also live usb creator in a windows VM works on the same install.
even though these are workarounds I can use, I think the issue should be addressed, as it might affect others. I am using a Dell 1340 4gig ram 500gig hd core 2 duo P8600 Nvidia 270.41.06.

Maybe you should address your concerns directly to the fedora dev team ?

Start by searching for your problem here and if you can't find your problem, then create a bugzilla account and submit a new bug. But be prepared to offer as much technical detail as you can. Read a few other reports to get a feel for the level of information needed.

I actually posted this(after searching) on fedora forums, and after four days of no activity, I figured they weren't interested. So I just thought I'd let you guys have a look. Maybe I have no patients, maybe I'm the only one with this problem, I'll wait and see, maybe I'll post a bug.