I am not interested in lying on the beach (though walking on them is fine!). Sounds as though the snorkelling is only fair. Is there good kayaking and/or hiking in the area?

I'm not much of a beach lounger either. Regarding kayaking, I've found this site http://www.zoekayaktours.com/ but also, there are several excellent Zihuatanejo/Ixtapa area websites that I have found very useful for an upcoming trip in January. (!!!)

www.zihuatanejo.net
www.zihua.net
http://www.ixtapa-zihuatanejo.com

These have been most useful so far. You will find plenty of activity options-- my only worry is having enough time!

As a regular visitor to Zihuatanejo I recommend www.zihuatanejo.net over the others including the one dominated by a certain Travel Agent who is constantly giving only recommendations that profit her.
PS I posted a bit to you on TripAdviser also.

Go with zoekayaktours. We have done it twice and really enjoyed it. If you love nature, bird watching, some moderate exercise and great food on the way back to the hotel, go kayaking at Potosi. We've also gone cave exploring and zip line riding in the tree tops. Not your typical beach vacation stuff. Enjoy!

Hijacking this thread to ask some related questions..
1) if you aren't a 'bird watcher' would it still be fun to kayak?
2) anything 'jungly' to do...zip lines, hikes, etc.?
3) whale or dolphin watching? our group usually rents a boat and snorkels and has a fabulous lunch, but sounds like snorkeling is not so great, so would there be such boat tour for whales or dolphin watching plus exotic lunch? thanks..