I've seen mentioned in several posts using metamagic to gain additional power points. Is this actually in the rules anywhere, as an option or otherwise, or is it a house rule?

It is found in the Errata for street magic on the main shadowrun homepage. http://www.shadowrun4.com/resources/index.shtml#errata

The one place I hadn't thought to look. Thanks.

Well its also in the list of optional rules in the newer printings of the book.