This is a real grumble.
You can read below about our cruise in March 2012 to the Canary Islands. The trip was marred by an ongoing outbreak of Norovirus on the ship. Many passengers were affected, and part of the remedy was to ask them to remain in their cabins for 48 hours. As an incentive, there was mention of a discount on on a further cruise for those who comply. As a precaution passengers who might not have been affected, but showed symptoms were also asked to comply. My Mrs was one such - it cost her two days of a 12-day holiday, and myself, too to some extent, although I was able to make more of the time since I was able to leave the cabin and go ashore as well as sitting and keeping her company.
The voucher for a future cruise discount had not arrived by mid-August, so I wrote to ask why not. To be fair, the reply was very prompt, and came with a voucher for £61 off a future cruise, valid until the end of 2013.
Now £61 compared with a ticket price of £1259 amounts to a discount of 5% for one person. Better than nothing I suppose, in monetary terms, at least. Worse than nothing in terms of customer relations. I doubt whether we will use it. I just negotiated a discount of more than 5% for two on our next cruise, but with a different cruise line. I don't think we will be using our Fred.Olsen voucher.