Old school, the same rule applies for networks as it does hosts, i.e 2^x-2 (x is bits)
Most hardware now allow the lower & upper (all 0's & all 1's) bits so it does work. The key is MOST. I have never come across them not being able to be used. Cisco devices have a command to turn this on (IP Subnet-Zero), this basically allows the additional range to be used.