The hop on, hop off bus is definitly worth doing, the buses wait outside the port building and can be booked inside the building, so very easy to use and go everywhere you would want to see in Dubai.
We wanted to go up the Burj Kahlifka but found all the slots were booked, luckily we had another day in Dubai, but there was only a couple of slots left - you can book this before travelling so not to be disappointed.
We did the additional evening trip around Dubai through the same bus company, an additional Â£15, but worth it.
We walked 5 minutes from the ship to the port gate and found lots of taxi drivers - going rate seems to be about 50 US dollars for 4 hours per taxi - although be careful, it soon became apparent that the taxi drivers have arrangements with some shops and we were taken to several shops between the places of interest we had asked to visit.
All shops, markets, taxi`s will accept US dollars - take lots of small notes.
We walked the few minutes to the port gate and hired a tuk tuk and found it a wonderful experience. The drivers were polite and friendly, they all have a list of places of interest to visit so we left it up the driver and were not disappointed.
Always haggle about the price of the trip - I think its expected.
The only thing wrong with Cochin was we were not there long enough!