Alien Skin Software just released a free update that packs a bunch of new features into Blow Up 2. Don't be fooled by the tiny version number 2.0.3 because there is juicy stuff in there. Go to the Blow Up 2.0.3 update web page to download it.
Blow Up now appears in the Filter menu. An even easier way to start it is through the slick new Photoshop CS4 Startup Panel. The panel resizes your image to standard paper sizes with a single click, including ISO sizes like A4. There is a new performance slider in the preferences panel for optimizing Blow Up for processing speed or memory use.
Blow Up 2.0.3 also installs a Gallery Wrap Panel for Photoshop CS4. Although this panel is installed with Blow Up, it does not rely on Blow Up to work. So, even if you don't intend to use Blow Up, you can install it and then just use the free Gallery Wrap Panel.