I am try to create a big excel 2010 with 30 columns and 1 million records with Apache poi latest. I am creating as describe in this link http://svn.apache.org/repos/asf/poi
I would also suggest you look at using sxssf. It uses an xml format to load it into Excel. This is much faster and a better way to create large reports or grids. The autosizing function in xssf takes too long by default.