if you have a domain name that you like, but .com is already taken, would you choose .net? or would you try to come up with another domain name so you can have .com?
The danger with getting a .net in place of a taken .com is that your visitors may get confused by the name and end up on the wrong site. I'd re-think the name if you can.
I was setting up a site for TV station (lets call it K123) but k123.com was taken (by a porn site non the less), and k123tv.com wasn't available either.
We settled for as different as we could: k123.tv - it cost us more, but set us apart from the, eh, "competition", while still maintaining our branding.
Mikko is right. If you are using your business name, then you might try and seek out a slight modification to the .com to get you through. Branding is very important, and if you have an established non-net brand, then you need to apply some lateral thinking. Remember, if you are applying a branding strategy, you will be dropping your new domain name on all your bus stationery, advertising, etc, confusion is the last thing you need as someone eyeballs your advert on the side of a bus and ends up at the wrong site when they get home.
You might want to put a clear business double barrel such as (for example ficticious generator business) viking-generators.com instead of viking.net or vikinggen.com or similar.
.net does imply network based businesses. go the .com and some reworking perhaps.
If you are using the domain name as a new business name from scratch, then rethink the name rather than struggle with a single idea that you may not be able to run with.