You will find that types can contain very useful methods. To get a list, you can pass the type to Get-Member, but do not forget to specify the -Static switch. Without it, you won't see the static members, but instead just the (rather useless) instance members of the type:
[DateTime] | Get-Member -Static
[DateTime]::isLeapYear(2010)
[DateTime]::isLeapYear(2010)