Yes, Having a faster GPU can help when using some effects in Final Cut and some apps in the CS4 suite can off load work onto the GPU. Photoshop doesn't do much other than "fly" when panning through an image. After Effects can off load some of effects onto the GPU as well. Also I'm not sure if it made it to the mac side but Media Encoder CS4 (which AE and Premiere Pro use) can use the GPU to speed up h.264 encodes, again I know it's available on the Windows side of CS4 but I'm not sure if this feature is available on the Mac side.
Even iMovie can use the GPU to render thumbnails.
At least get the GT120, you will be much happier in the long run once GPU off loading becomes more common in apps.