How much is too often?

[#1]

I was wondering how many router reboots is too often as far as BT is concerned.
It doesn't affect me directly as I tend to leave me router turned on all the time, but I have a mate who turns his on and off depending on whether or not he's using his PC, which could be two or three times a day.
Would BT count this as a loss of sync and downgrade the line speed, or do they only count disconnects and immediate reconnects as a loss of sync?

[#2]

On a stable line it'll take multiple disconnects in an hour or so to affect speeds. On a less stable line it will have more of an impact. Evening resyncs tend to be worse than early morning ones.
A lot of people turn their routers off overnight with no issues.
Does your friends connection stay up when he leaves the router on? Does he have decent speeds when the router is on?