For those having trouble getting Cydia via the GP Loader, just let redsn0w install it (don't choose the Monte option)
(The reason that works is tethered RS doesn't touch boot sequence at all, but GP does. They stay out of each others way)
Hopefully this will not be necessary once traffic settles down. You can download RedSn0w from here.
As a side note, those who are currently running a tethered jailbreak can reportedly install GP over their tethered jailbreak to become untethered; although a clean restore is recommended.