It is preferred that the name you want is available (especially as a .com) and in other areas (such as twitter or facebook) as you have mentioned. It is particu

It is preferred that the name you want is available (especially as a .com) and in other areas (such as twitter or facebook) as you have mentioned. It is particularly important to make sure it isn't trademarked. That said, it's preferable, not required. Obviously a lot of companies don't use a .com, don't necessarily have the exact domain (delicious being an extreme case originally) and can still make it work. It's all about branding. The main thing you would lose is organic type-in traffic. There's still room for creativity though.