I've used over 500 labels on my DVDs and have had minimal problems. A few of my oldest DVDs (1-1/2 years old), have had some playback problems, but it's hard to say if the label is to blame. Back then, I used any old cheap media I could find. I think any problems were due to the cheap media, or maybe the combination of cheap media and labels.
For over a year, I have used only TY or Verbatim media. Since then, I've labeled over 400 disks with Zero problems. I've been using the glossy labels from Meritline.
That said, I recently started printing directly to disk, and I love it. I think the results look more "professional", and you avoid any possibility of label problems. I find the printable (TY) media to cost about the same as a regular disk plus a label, so cost really isn't an issue.
I have a Canon Pixma 5000 printer (US version). I recently did the firmware and registry changes needed to defeat Canon's disabling of the disk print feature. Then I ordered an official Canon print tray from eBay. (Others have made their own trays, but I'm not very good at that type of thing.) If I had it all to do over, I would have just ordered the non-US version. The Pixma 5000 is an awesome printer, and now that I can print direct to disk, it's even better.