Re: How many ?
"many industries require burstable systems."
Would you mind name at least 5 ?
What confronts me and my team are:
Time and expense systems - at end of month everyone logs on to do all the work they should have done in the month
ERP systems when doing end of month reporting, or trying new cube/datamart based data analysis
And separately ERP systems when people do very large MRP roll ups
Transactional web sites when the company is offering sudden discounts or at the end of bidding by subcontractors. These aren't general public facing
Less so as this can be predicted - mathematical modelling of business processes and trying different parameter sets.