You still could consult Foster's book about assertions (and forget that he works for Verplex), it is more or less usefull.
Unfortunatelly we use asertions in very limitted way (not really assertion-based design, but only some protocol checkers and similar things in test environment). It saves us a lot of time somethimes, but we don't have lots of them, so there are no false fires and simulation slow-down doesn't exist.