It looks like Sun will soon deliver on their promise to allow the services that drive their Sun Ray thin clients to run on Linux. Coupled with the ability for desktops and laptops to act as Sun Ray clients, this feature will make the UBA architecture a very attractive proposition for mid and large-sized companies (even though I fear that Sun Rays for Linux will only run on a server version of Sun's JDS).
If Linux gains better integration with Active Directory (Kerberos auth for cifs network shares, a better ldap_nss or an easier way to share uids/gids with winbind) it could really become a serious threat for Microsoft in the corporate desktop market.