what is your hardware ?
for example i have a VERY old box with a p4 ( from 2001 ) a gforce2 ( yes 2 ) nvidia card and 1 gig ram
ScientificLinux 6.3 boots up in about 1.5 min.
from push "power" to user is logged in
as "jpollard" said NFS can take time
and so can the network connection
-- How are you connecting to the network ?
install"bootchart" it should be in the RHN repo
yum search bootchart
---- then if listed ----
yum install bootchart
then see what is causing the problem