.Com woops .net out of the park. Depending on the name, you could get 10X + for a com compared to a net.
I personally don't think it matters too much although more people tend to instantly thing all web addresses end in .com
Basically for type-ins, people would tend to add '.com' to the domain names when typing in the URL rather than the '.net' option so you may be losing traffic if there is already a .com variation of the domain name. So if there is the .com option which is still available, go register it. You can block others from making variations by buying all the commonly available TLDs for the domain name in question. However for search engines or directory listing, the .net variant does not make much difference to the engine.