The worst colection cds are the "20,000 tunes from the emerald isle" or "groovy celtic chillout" ones. I bought one ages ago cos there were a lot of tunes I didn't recognise and I thought some might be worth learning. It was literally hours of plastic leprechaun stuff played alternately by about twelve men they'd obviously pulled out of the pub at midday in the vain hope that they'd be sober enough to sing and by some sort of wannabe operatic tenor. brr! Gives me shivers just thinking about it. Cheap Waterson/Carthy CDs sound very interesting though.