What's the total cap on number of Primecoins, or is there one?
The end of the coindesk article states this:
The group behind the peer-to-peer cryptocurrency, PPCoin, think it has the answer with Primecoin. There is a detailed paper [PDF] on the website, explaining how the currency works. It shows that the proof of work in finding prime numbers is computationally efficient. However, this is on the proviso that the prime numbers are not record-breakingly large.
This is where there is a question mark over the value as it isnt made clear whether there are still prime numbers, other than those that break the records, to be discovered.