When you are registering a domain you are planning on doing a site with do you buy the other TLDs as well? For instance, if you get the .com for a site do you also get the .net, .org, etc? I sometimes do and sometimes don't. I don't have any developed sites at the moment, but was thinking about this when going forward.
I used to do this for every domain I registered, now there are so many tlds that it would only make sense if you had something big
Pretty much what NoxServices said. Personally I'd just take the .com and, if you're offering the services to the UK aswell, take .co.uk
I dont bother with the .net or .org but have now found myself beginning to purchase .co.uk's to match the .com's that i buy.
I just did this for my main site to protect it. Picked up the .info too since it was only $2/yr as well and since it's a two word domain I picked up the firstword-secondword.com too. I wouldn't do it for any other site unless it was developing into a 'brand' of sorts.
It will depend on how much I like the domain im registering. 9 times out of 10 I will register the other extensions.