If you're actually developing the .com, having the .net isn't a bad idea at all, esp if it's a more generic term you can't really trademark. You might wake up someday and see a competitor operating on that extension and think, "dang, I wish I had vanquished them to the realm of needing to use .info, or choosing a different name." In that case, it's definitely worth the $10.
If your .com is REALLY good, and you're able to get the .net, it just means any end-user has one less path to take that doesn't lead directly to your door.
I know somebody with a god-tier .com, who recently paid a few grand for the matching .net, and I think it was a very wise investment. It's kind of like collecting property in the board game Monopoly, once you have one of them, I think the others can become more valuable to own... but only if your .com is good enough. I wouldn't go and start buying the .net's for every .com that I'm hoping to sell for $300 or $1000.