I see a few minor problems. First require 5.6.0 is not a good idea. You probably want something like use 5.006 instead. The require should execute after the use warnings, not what you want. Also the ability to use 1.2.3 type version strings was not avialable till perl version 5.6.0. You might want to consider even trying to make your module work on perl 5.005.

As for your hardware_info function, I think you could improve it by caching the hardware info, only computing it once, rather then recomputing the same info three times if someone calls model_type, processor_arch, and processor_speed in succession.

I wonder if you really want to call your module AIX::SysInfo, or similar.

As for your export list, it's not a good idea to export so much by default. Try to limit or eliminate your default export list. You also have declared an export tag which does nothing. Best to get rid of it if its going to do nothing. </p.

Additionally, Sys::Hostname already exists and is standard. Your hostname function is not worth much.

If you want to be paranoid, you should be checking the return values of the various programs you are calling after the close of their pipes, in case something goes horribly wrong, and maybe checking if something goes wrong with your backticks.