Business Perfect URL Stamp by LetterGirl
3 very good reasons to buy your shop's domain name:
1) If you don't, someone else might grab it!! This might impact on the way you come up in google search results, and means you can't use the name later if you decide to start your own website.
2) It can look more professional to have a .com address on your business cards etc, even if it just leads to your etsy shop.
3) This one is very important and I only really realised its impact when I recently set up my website morphologicadesign.com . We spend so much time and effort driving traffic to our etsy stores and building links etc over the years, but all of that is tied to etsy. If you ever want to change to selling on your own site or if etsy ever disappears, all of that hard work will be lost! By having a domain name that points to your etsy shop, you can take all of your links with you if you ever want to and you have control over all of that traffic (links also impact generally on your google standing). The same applies to your blog- that's why I changed over from the blogspot name to a .com URL.
So where can you get hold of your domain names? I use GoDaddyfor my .com domains because they're cheap and well established/reliable (they're good for domains but I'm not sure about their other services). For Australian domain names, jumba.com.au seemed to be the best when I was researching it, so that's what I use for my .com.au addresses.
Don't forget you can pick up more business tips on twitter @etsysellertips