The folks at SQLTeam have done some analysis on different ways of importing text files, you can read the info here;

http://weblogs.sqlteam.com/mladenp/articles/10631.aspx

http://weblogs.sqlteam.com/mladenp/archive/2006/07/22/10742.aspx

And of course Gert has a ton of good data on high perf loading here;

http://www.sqldev.net/events.htm