how old are you looking?
if you are looking at the mk3 then yes,look out for :
noisy dual mass flywheel on start and shut down,
clunking noise from rear over bumps,
sagging rear bumper,
injector failure is expensive but not that common,
egr valve blocking, simple clean, will flash the glow plug light as a warning.

but other than that fantastic cars, they have their faults but generally if you buy a good one with service history you cant go far wrong,

if you are after the mk4, they are extremely spacious inside!
i dont know alot about their reliablity etc but had one as a company car for 5 months and loved it.
very comfy, very economical, and very big inside!