The USCIS has increased the admission period from one year to three years for Canadian and Mexican nationals. The rule also provides three year extensions for qualifying workers. TNs can be issued by Border Officers or if the worker is in the US, by the USCIS.
TN visas are available for dozens of Canadian and Mexican workers. The full list of acceptable jobs can be accessed here: http://www.nafta-sec-alena.org/DefaultSite/index_e.aspx?DetailID=167#Ap1603.D.1
The three year period is also expected to add extra practical flexibility for Canadian and Mexican nationals who are seeking US permanent residency (green cards). Please contact your HLG attorney if you are interested in discussing the applicability to your immigration matter.