I work (as an atco at a busy commercial airport) near a very busy gliding site (in East Anglia), we have an excellent working relationship with them, and whilst their r/t procedures probably aren't the best in the world (due to lack of practise etc), their airmanship knocks the spots off the majority of PPLs who operate from the 25 or so airfields of varying sizes in the vicinity.
Even with strong upper winds, they make a concious effort to avoid the instrument approach lanes, which is pretty good of them considering the traffic levels and types of large jets which we handle, and that we are in the open FIR and only have an ATZ.
Obviously, the vast majority of gliders don't carry transponders, but still paint a strong primary trace on the radar, so we can take avoiding action if they're not seen.
My only other comment would be, if you have a radio, use it and let us know you're there, listening out and monitering the frequency without talking is as much use to atc as a chocolate fireguard.