The .com might make it easier for people to find your site because people are more familiar with that, but the difference may not be very significant for you. There are major sites that use .net instead of .com like http://www.leadpages.net/.
Thanks, SuzannaK!! The .com version isn't being used, it's just owned by someone who's sitting on it and is selling it for $2900, which is a little much. I really like the name, though, so I may just go the .net route. I just have this weird hang up about it.
I think ideally you'll snag a .com - it's just more professional (in my humble opinion) and Suzanna makes a good point.
One thing to think about is if the .com is owned by a business offering VA services you could potentially run into trademark issues (not too common in our industry but it does happen...)
At this point (with high market saturation and very few truly good .coms left to buy) I recommend if you can't get what you want, pick up yourname.com and brand around your SELF
I'm my opinion it really makes no difference what extension you have assuming your website can be found.
The problems come when you are running a site and the .com is in the same business.
Having said that, a lot of the decent .com's have been purchased and brokers are sitting on them trying to make a few £'s as the OP has found.
If the .net is available and you really want the domain name then buy it, spend time creating the site and filling it with decent content, and make sure you employ strong SEO so that you can rank it as high as you can in Google listings.
Or, failing that, keep searching for a .com that is available o as Tess said above, market as yourself.com