I ordered tickets for the San Marino GP next weekend about a month ago from GP Ticketshop. There website quotes I will have the tickets 2 weeks before the race.

With a week and half before the race I still don't have the tickets.

Problem 1:
With Friday and Monday a bank holiday and I am leaving for Italy next Wednesday, that leaves tomorrow, Thursday and Tuesday to receive the tickets

Problem 2:
They don't reply to my emails!!

Apart from calling them which I plan to do (at my expense), what could the potential damage be???

Thanks,
Alex

Like you said, call them, call them, call them.

Other than that, print out everything you have (emails, ticket confirmations, credit card statements, etc), and head directly for the ticketing office once in San Marino.