If you have any workaround for the G2/G2s, please add them to the Wiki page I'm maintaining on reprap.org:

http://reprap.org/wiki/Delta_Rostock_mini_G2s

I've included fixes for a bunch of mechanical issues, including:

Mechanical Rigidity:

* Ensure the frame is rigid - if not, add washers to the smooth rods
* If you have a "wiggly spider", buy or print out the shim washers for the rod-end holders.
Frame
* If you can't finger-tighten the 4mm bolts into the smooth rods, don't force them - the blind thread may be too short. Use washers to shim up the bolt instead.

Belt Jams:

* Make sure both set screws in the driving pulley are secured.
* Make sure the idler pulley wingnuts are fully secured.
* Add idler pulley washers.

Homing Issues:

* Verify that you are on the correct pins for your endstops (see end of manual for correct pinout - earlier photos in the manual are incorrect!)
* Separate and twist the endstop wires to prevent false homing triggers

Bed Levelling

* Put lock washers under the bed wingnuts, so that you can adjust the bed from the top using the allen bolts.
* Ignore the autolevel feature for now - the printed guide for the probe can be too tight (or loose), and cause a head crash on autolevel.

PEEK J-Head

* Verify that the teflon guide is the correct length (if your PEEK cylinder is touching your heating block, it's too short!)
* Heat-tighten the PEEK heads to prevent leaks
* G2s: Align the nozzles to prevent interference during prints

Extruder:

* If you are getting under-extrusion (unexpected random holes in your print), make sure the Mk-8 extruder's tension is set correctly.

PLA Specific:

* Put a fan next to the bed to improving bridging and prevent blobbiness

ABS Specific:

* Use the correct Beta (3950) for your thermistor, and PID tune it (someone with Marlin experience can expand on this) - otherwise the PEEK heads will melt with the default firmware at 240C
* Add insulation under the heat bed to prevent heat loss