I'm not sure about Nikons, but long exposures are nothing to sweat on a Canon dSLR. I routinely push my exposures up to the half hour mark:
http://www.digiteyesed.com/portfolio/image...05/01/00300.php
http://www.digiteyesed.com/portfolio/image...04/11/00009.php
http://www.digiteyesed.com/portfolio/image...04/10/00022.php
I'm not the type to shoot concerts and bars at high ISOs, so you'll have to talk to someone else about that. :-)

