Switch & connection

I just replaced all my hubs with switches. Everything went pretty smoothly. My Netware network seems to be back up and running fine. I just can’t figure out why some people find the network in the morning, but if they have to reboot during the day, when the PC comes back up, it can’t find the network. If you go to the switch, find their connection, remove it from the switch and patch panel and plug them both back in, reboot their PC again, it finds the network fine. Are switchs more sensative then hubs? or is it just a the fact that maybe it didn’t have a good connection when I made the move from hubs to switches?