What's cool is that there are many unique approaches to creating a pumpkin shape, really. I just figured out one way on my own. Below is a demonstration of another way that Googler Aidan Chopra makes pumpkins, using complex curves.
1. FOLLOW ME the arc around a circle:
2. It will look like this when you are done:
3. Erase all but one segment (see below) and use the SCALE TOOL to enlarge the center spine (in red) by 1.15%
4. Use the scale tool again on the other two spines at 1.10% (in red, at left). The finished component is on the right.
5. Now COPY-ROTATE the component around into an upside-down bowl shape (similar to step #2's appearance) and then group everything. COPY-MOVE the whole thing beneath the original, then use the scale tool again to scale that one backwards (until it is looks like a right-side-up bowl shape) on the blue axis. Type "-1 ENTER" to get the dimension exactly right. Then match the bottom half to the top half with MOVE tool, and paint!
*EDIT: The contest sites are no longer live, however the 3D model collection of pumpkins can still be viewed HERE.