Depends how serious you are about your brand. For the $8.99 it costs you a year, there is no reason not to in my opinion. If you don't a domain squatter will buy it up and charge you a couple thousand if not more later down the road, if your company turns out to be successful.
Heck, I'd even go as far as suggesting to buying any typos of your domain. We own Tether.com and a domain squatter bought up Tehter.com and Teather.com. Now we pay $5-$10 a day to advertise on those domains to get that traffic back to our main domain.
In my experience - Getting the other extensions is a waste of money. Here is how people generally find your site:
When we first started our company, we registered misspellings, and all the similar .net, .org, .etc domain names. A year later, we decided that it was $200 wasted every year on pages people never visited (we got 0 visitors to almost all of them)
Log what domain name people use to get to your website, and see if anyone is using the .org, .net, .biz or .info. If so, then you might consider keeping the ones that are getting used. If not, then I'd let them lapse -- you can't stop someone using your name in their domain unless you also register a couple of hundred different country-specific TLDs, plus the new generic TLDs that are expected to launch soon.
Seriously, register them. All of those domains are cheap to register yearly and it'll stop some jerk mooching off your name with a link-farm trying to cash in with some AdSense ads. The internet is full of jerks and squatters, you'll find that out sooner or later if you let those other domains go back onto the domain market.
Absolutely yes. You will be very upset when your business is successgful and someone registers .net or .org and there will be nothing you can (are willing) to do about it.
Since you dropped the name, a bastard like me will register jitbit.org, jitbit.net, jitbit.us and others, build similar sites, and try to mooch off some of your traffic!
If you can afford them, register them and point them to your existing site.
If you are in a niche it might be worth protecting your niche from other entrants on the SEO work that you do with the domain (if any).
I think we've forgotten the days of $70/year .com registration. Spending the same per year now on a handful of domains to protect the space you've worked hard to build and grow traffic to is something I'd think about twice, especially it was a niche.