Can you elaborate? All I know about Telerik is that they do a lot to sponsor community podcasts and user groups.
Well RadControls as a fine example: bloated, unreliable, impossible to work with, buggy, slow, expensive.
The above may all be true, but I'm sure you'd say the same about any of the "enterprise" suites of web controls. Speaking from experience with Infragistics, I'd say the exact same things. Perhaps it's the price to pay for trying to make the "be all and end all" of control suites.