i have had no bugs with 3.40 except when i used custom xmb icons however the decrypted ones solved the problems. currently theres only 1 reason that's valid to not upgrade and its that some homebrew (like pimpstreamer for example) will not work properly or at all. theres another possible reason to not upgrade if you have loads of homebrew and that's because some of them will need to be converted to work correctly. this is an easy process but is a little time consuming.
to me however the benfits outweigh the drawbacks (even if only just)