Are personal trainers worth it?

Are they? I have never had one before. At the local gym they have set groups (6 in each group) that meet with the same personal trainer who works with each individually with a diet plan/checks your weight/strength training/body analysis/ health analysis/gives you input on your food plan notebook which you have to keep. I used to do weightwatchers and really enjoyed the weigh-in because it made me feel responsible for my weight and I lost quite a bit. Then I had an operation on my ankle and am looking forward to the training sessions but s it worth the money (it isn't cheap here and you meet for twenty weeks).