No hot water at faucets after replacing water heater
Check all the supply valves to ensure they are open. 

It is not uncommon for old valves (particularly gate valves) to break whilst operating, leaving you with a low or no-flow situation (sometimes called a "dropped wedge"). This would require you to replace the suspect valve. If you did a DIY install, were any of the valves particularly corroded or hard to operate?

It is also common for debris to be dislodged during the work, causing plugging of downstream faucets (although this would be unlikely on large faucets, such as a bathtub filler).

Did you shut off the main supply valve to the house or out at the meter and forget to turn it back on? If a plumber installed it, call them back right away.