If you encrypt stuff, better use a method with strong cryptographic properties, very large key sizes, and make sure you're not running compromised software (e.g. anything by Microsoft or Apple) or using compromised web services (e.g. anything from Google, Facebook, Yahoo, Skype etc).
I wouldn't be surprised if the NSA can routinely decrypt some of the popular encryption methods, using a combination of brute force (probably they have very neat dedicated hardware just for brute-force decryption), weaknesses in the method itself that have not yet been discovered by the public, and subtle weaknesses in particular implementations of the method (subtly introduced or silently discovered by the NSA). While I don't think the NSA has secretly discovered that P=NP (that would be neat though), it's still possible that they have found an efficient decryption method for e.g. the RSA problem (which is not known to be NP-complete).