From what I've seen, the MacBook Pro revisions alternate in technical and specification updates. Technical updates generally focus on component upgrades, while specification updates generally focus on increasing the spec of the existing components.
January 2006: Technical (Intel, new GPU), small HD bump
October 2006: Specification (RAM, VRAM doubled), big HD bump
June 2007: Technical (LED, Santa Rosa, new GPU), small HD bump
February 2008: Specification (VRAM doubled), big HD bump
October 2008: Technical (new chipset, case redesign), small HD bump?
So I don't expect a big HD bump for this revision.