There's thread on stackoverflow about this http://stackoverflow.com/questions/5524046/is-telerik-extensions-for-asp-net-mvc-free
It says that it is ok for internal site, but I think it is still not clear (also in faq notice about internal site usage is gone I think).
They say, as long as website is internal, you should be ok with open source license, but
1) Can I use it for site, that has closed community, I mean only logged in people will use telerik components?
2) Can I use only for site's administration part, that means that only internal staff will access it?
UPDATE: It looks like same question (same license type) - Using GPL libraries without modification on a commercial website, do I need to make my source code available?, but answers are completely different?
UPDATE2: I don't wish to in any way distribute site's code.