The pricing remains at $29US for a single user upgrade, or $49 for a Family Pack upgrade. You can only install the upgrade edition if you're using Leopard. If you're not, you'll need to buy the Mac Box Set, available for $169 for a single user or $229 for a Family Pack.
Before you install, check out our upgrade guide. Also, note that If you purchased a qualifying Mac on or after June 8, 2009, that does not include Mac OS X Snow Leopard, you can upgrade for $9.95. Thanks to everyone who sent this in!