Err... I'm no expert here but I think you'll find most OO implimentations (including C++,Java) tend to just keep a copy of the current objects instance 'stack' in memory (instead of the the entire code base as well).

The only exception to this rule tends be be in the unavoidable areas such as serialization etc.

I'm not saying that it doesn't tend to chew up memory but in these days of relatively cheap memory, I suspect most people have put a larger priority on running speed than memory usage.

Not that I've ever done it in Perl, but you may wish to investigate techniques such as pooling and proxies if memory usage is a concern.

Update: Forgot to mention that there must be at least one copy of the class/code for each different object type/class/thingie/doodad.... er see below. :)