Genuine Fractals has long been the choice of many photographers who wish to print their images larger than would normally be possible without interpolation. OnOne software claim that Genuine Fractals will produce sharper, more detailed prints than those interpolated using the resizing tools built into Photoshop.
The last time I used Genuine Fractals, it was a standalone program. To interpolate a file, I would have to first convert it to the Genuine Fractals .stn file format, which I could then open in Photoshop via the plugin at the new interpolated size. The main issue I found with this solution was that my hard drive would end up littered with .stn files that I couldn't browse properly in Adobe Bridge, so they would sit there hogging space on my drive.