Pointing both domains to the same place essentially creates two URLs with duplicate content. In a search engine’s eyes, it will take longer for them to catch on that the two sites are one and the same, and for a time you’ll probably have different rankings for each version (and also different incoming links).
This dilutes the power of each page.
The 301 redirect is recognized by most search engines and ensures that links and rankings for either TLD are applied to only one.
Redirect the com to the org with a 301 as mentioned and you’ll be fine. Having the com is a great idea though - when talking to some students about the robocup competition, you’d be surprised how many people in the room immediately visited the robocup.com website on their laptops (the site they were looking for was robocupqld.net.au) before I even gave them a URL.
I believe that each TLD has a specific advantage in it’s area.
For example .com’s are considered to be commercial sites.
.net - networking
.org - non commercial organizations
and so on
But there are some TLD’s that have main advantage, for example .gov .mil and .edu
Yes, its funny how peoples minds work here, they pretty much expect you to have the .com of your domain.
I have a client who could only get the .org name for his website. I swear, every single time… I type the name, hit ctrl-enter and go the the .com site of some band. If I could only remember to hit ctrl-shift-enter instead… lol
I think that if someone is hand typing a url they are more likely to use the dot com.
I believe even today most people correlate a .com with a business for profit and a .org as a non-profit.
maybe use the .org for news or something to give back to people(industry news, free info ) with of course a link to your sister site, the .com
It’s been said that .org and .com DO have SEO advantages. There is nothing to lose in getting a .com name, especially.
Plus, the ctrl+return shortcut (which adds “.com” at the end of the text in the address bar of browsers) works for .com domains 
Btw are there shortcuts for other TLDs, I am not aware of?
Pretty much what this thread is about it that there is no advantage to any TLD in SEO. It’s just a myth.
I’d use the .org for community and .com for commercial support.
I would definitely go with the dot com as that is still the most known and respected domain extension.
ok You guys are going in circles. With the .com / .org ordeal so i will shed some light on this subject. First of all search engines really dont care wether you are a .com or a .org.URL’s translate to an IP address and thats whats fed into the crawler wether is google or yahoo or any other. The fact that your domain is a.com or a .org should not matter for the crawler sees 4 octets thats it. no prefferences toward a specific domain, why cause it simply does not follow a domain it follows an ip address.
I’d use .org
There will be a lot of .com type-in traffic so just redirect that to the .org version. 
Since the nature of your site is open source, I’d go with the common usage that’s been prevalent thus far and use the .org (& redirecting .com traffic to .org as well).
I have a World Peace site with a .com and have the blog with a .org. The donations are greater at the .org, only reason I can come up with is that people associate the .org with a non-profit and therefore feel more at ease about giving. Tracking shows no difference in demographics or referrals telling me that the SEs have no preference either.
Both .com and .org are good. Take both or as per availability. Sometime .com not available, better go for other extention.
Someone is most likely going to type .com if they type it themselves.
Just do both.
personally i prefer .com for any site if possible.
many opensource projects also using .com
.com tend to have higher monetary value in domain industry
anything relate to internet, people just add a .com
to them .com means internet. i dont think as a layman user they will associate .com to commercial site. however, i believe they associate .com to internet or any websites.