1. Can you use the Icom OPC-1529R cable with Chirp and a USB-serial adapter?

Yep, should be able to.

2. If not which cable do I use - is it the Icom OPC-478UC and if so does this work without any drivers on the Mac OS? I'm not after cheap eBay cables - just reliable connectivity.

The OPC-478 is the older cable, which has a TTL converter in it. Their newer radios have started to support cloning via the regular RS-232 port that they now have. I can't say I've tried it with the 880, but as consistent as the Icoms are, I'd expect no issues. I have an 880 here, I guess I should check it :)

3. If I can use the OPC-1529R then does anyone have a USB-serial adapter which they are using on Mac OS 10.8.x with that cable which works well? If so which one?

From my experience, the KeySpan is the best one for your platform. It's big (although I wouldn't call it clunky), but it has a removable cable and does a lot of neat stuff that the others won't.

What chip/driver is in your Belkin? They're usually prolific, which is the most common, but also the most commonly problematic on MacOS, in my experience. I think Tom would argue for FTDI-based gear, but I'll let him speak up.

Just with respect to a current discussion on the list about Mac where it was suggested it is a "boutique platform" - I'm not sure that you can say that about the biggest selling laptop platform in the US for the last quarter ;)

Heh, I hadn't heard that, and I'm certainly skeptical of such a claim. However, regardless of growth, there's a lot of ground to make up. Further, due to Windows' architecture, some of the driver cores have been around longer than OSX has been a commercial product.

Yikes, I sound like a Windows advocate. Ya'll know I don't own a single machine with Windows on it, right?? :)