Whenever the SQL Server is struggling to write the transactions to the disk, you would observe WRITELOG wait type within SP_WHO2 results. So when you observer such wait types then you should be worried on the disks performance, either you plan for shrinking the transaction log (which is a temporary workaround) or add a second log file on a different disk. The reason behind for this wati type is heavy rollback activity adds additional log and disk I/O contention, and such activity has been observed...(
read more)
Read the complete post at http://sqlserver-qa.net/blogs/perftune/archive/2007/10/12/2452.aspx