Plumbing 101 - Reduce main supply to 1/2"

[millerama]

I recently had my plumber replace the main shutoff valve inside my house. Everything seems to be working fine, but I noticed that a section of the repair goes from 3/4" down to 1/2" and then back to 3/4" to the whole house (minus one outdoor faucet).

My question is, does this have any adverse affects? The water pressure seems ok, but I suspect that it is actually less than before the repair.

The original pipe was steel and the new section is copper.

http://www.terrylove.com/watersize.htm