Just bought a house. When using more than one anything in the house, the water pressure drops significantly. For exmaple: flush the toilet. While it's filling back up, the sink will just trickle water out. This is true for any 2 combinations of shower/faucet/toilet/washing machine in the house (basically anything that uses water). Doesn't even have to be in the same proximity to each other.
If using only one thing, the pressure is fine. I bought a pressure tester and hooked it up to the outside hose and it shows as 58, which from what I've read is normal.
This is a 2-story house if that matters.