[Boost-users] [date time] performant?

Hi, I've been browsing the online documentation for the date time library, which is a model of good documentation (unlike boost::test, for example) and it looks pretty well designed. I wanted to know if there have been any discussions or benchmarks of how efficient it is? Do people have any general comments on this? Some background: I've been looking at quantlib (www.quantlib.org) - a c++ library which performs financial valuation calculations, and whilst they use boost, they have chosen to write their own Date and Calendar classes. Dates, holiday calendars, period calculations, etc, are commonly used in finanial calculations and a performant library generally would add great value. thanks in advance, John McMahon