Here's a site that tells you why you shouldn't use serger thread for quilting.
http://www.thequiltshow.com/os/blog.php/blog_id/3800
"Most serger thread on the market is the cheapest type of spun polyester thread. When used on a serger, multiple strands of this thread are over locked, resulting in a strong and secure stitch. However, if used as a single thread for quilting, it is weak and fluffy. It doesn't make sense to put two dollars worth of thread onto a $300 quilt. Inexpensive serger thread has a loose twist, is not very smooth, has lots of lint, and is not intended for single-strand use."