For F#, I didn't know. It looks verrrrrry sweet.

For BigDecimal, my grief is that it makes code horrible (at least in my experience, I'm still locked in JDK 1.7).

BigDecimal has the problem I see with the rest of my griefs : it is possible to compute things correctly with code (obviously), but the way the code is written is ugly (and painful).

   BigDecimal yearly_amount = new BigDecimal("1000.00"); 
   BigDecimal daily_amount = yearly_amount.divide(new BigDecimal("12")); // Beware the rounding issue

Wouldn't it be nicer if :

   money<4> yearly_amount = 1000.00 EUR; // 4 decimals 
   money<2> daily_amount = yearly_amount / 12; // Beware the rounding issue !

Of course, this notation doesn't help much with rounding, but at least it makes the code easier to read. And trust me, using BigDecimal, doesn't prevent many people of making mistakes with rounding.