In Henderson v. Myler 2012 BCSC 1649 (reasons for judgment found here), the B.C. Supreme Court considered whether a handwritten note was effective and changed the distribution of an estate as set out in a prior will. The prior will provided that the SPCA would receive the residue of the estate (approximately $1.4 million). The note provided that the SPCA would only receive $100,000. The Court concluded that the note was not effective, and so the SPCA received the $1.4 million residue pursuant to the prior will.
A CBC news article on this decision can be found here.
As Georgia notes in her post, it is important to immediately prepare a new will or codicil if your wishes for your estate change.