I just got a Santa Rosa MacBook and am having signal strength issues that occasionally disconnects me.
Things I've noticed:
1) Changing locations definitely exacerbates the problem. Work and school are under DHCP, but my home network is static. I've had problems in all three places when I switch locations.
2) When I'm at home during these issues, I'm about 10 feet away from the router and I'm often at three bars. At school, I'm about 150 feet away, but I have direct line of sight to the access point. I fluctuate between all levels.
3) Plugging in definitely helps the strength level, but doesn't resolve it completely.
4) Turning Aiport On and Off doesn't help, but restarts do.
Other than that, I've had no issues with Leopard or the MacBook.