not really heard many problems with turbos on golfs so IMO there not a common fault, though i could be wrong?
most common faults seem to be window regulators and window regulator clips ( window drops )
leaky window washer (causes boot lock to break)
doors dropping a little which can make it harder to open and close doors smoothly.
MAF sensors and Temp sensors.
and well yeah as daz said have a look through this section, and in the maintenence and info part im sure theres a buyers guide which will proberbly tell you all of the common faults, but the four ive stated above seem to be the most common.