I have an mid 2010 iMac running Mac OSx white stuff Leopard and it works great. Since the new standard of Mac OSx Lion, I've been reading lots of reports of "not recognized modem", dropped wire connection and even dropped wireless connections. Some folks say its the Mac OS Lion, some say its the different Network Cards in the 2011 iMacs and some folks say its the Cisco Linksys modem (yet, that same modem works perfect with a Windows xx machine).
A few moments ago, I found an interesting Cisco site. Cisco Linksys and iMac OS Lion "Cisco Connect" upgrade chart. If you have an iMac running Mac OS Lion (to plan to upgrade to Lion or future Mountain Lion), surf below URL. Your specific model of Cisco Linksys modem may need special Cisco Connect software for your iMac system.