There is some overhead associated with object oriented designs in Perl. The easiest to explain is the fact that objects are usually based on hashes, and hash lookups have a little overhead associated with them. Autoloading can also take a little time, inheritance tree searches take time, and so on. How much overhead OO adds depends on a lot of factors, and 30% is a pretty broad generalization. 30% as compared to what? Non OO designs will have their own complexities and own issues to deal with too. But yes, there is some performance hit.
The bigger question is do you care? If an OO design is the right design from a programming and maintainability standpoint, use it unless you can actually demonstrate that you've got a performance bottleneck that is significant enough to be concerned with. Chances are that if you've got code that's not meeting its performance requirements you've got the wrong algorithms or the wrong approach to a problem. You won't know until/unless you profile your code. Use/test your code. Then if necessary profile it. Then if necessary optimize it where the profiler tells you to direct your efforts. We all know what they say about premature optimization being one of the basic evils of the universe. ;)