Last year I received a few pumpkins off freecycle, and I saved some seed. All the pumpkins were of similar size and shape. When I planted the seeds this year, this is what I got:
Plant A) Mid-sized orange pumpkins (like the one on the left). Except that after I started scraping out the roasted flesh, I discovered that I did not, in fact, have a pumpkin. I had a spaghetti squash.
Plant B) Small, round, very orange squash. I haven't checked out the inside yet. Hoping it's pumpkin-like!
Plant C) Large orange squash.
Plant D) Large oblong zucchini-type squash with hard skin. And yes, it's starting to turn orange!
So after I noticed them starting to grow differently, I was reading my Organic Gardening magazine and discovered something very important about saved seed. The general idea is that you can't save seed from home-grown squash, unless you only grow one type of squash. Reason? Cross-pollination. The flowers from two summers ago must have been pollinated by various other squashes in the garden, thereby causing the seeds to have a different genetic code than regular pumpkins. So the original pumpkins turned out normal, but their seeds were...not. Anyway, I'm interested to see what the insides of the rest of these will be like!
On a side note, I used the spaghetti squash to make our Thanksgiving "pumpkin" pie and it turned out quite tasty!