Some (me included) will find that their PCMCIA modems mysteriously stop functioning under RHL 6.1, while the Ethernet part on the same card may work fine.
The problem is not with PCMCIA, but with the hardware detection utility (kudzu) that RHL 6.1 introduced.
The fix is simple - edit /etc/rc.d/init.d/kudzu and change
/usr/sbin/kudzu -t 30 to /usr/sbin/kudzu -t 30 -s
This stops kudzu from initializing and "freezing" the serial port configs.
The same fix also takes care of some machines that keep\ finding/losing their serial port mouse (usually on /dev/ttyS1 - COM2 for DOSsies).
This information was found at the *old* PCMCIA forums, so I thought it may be useful to people who only come to the new forums here.