First of all, when it comes to variations, you'll have access to all the subdomains that you could ever want, so choices of variations are at your fingertips already. e.g. i.areallygood.com iphone.areallygood.com, my.areallygood.com
If you have .com, that's the primary name to have control over.
Misspellings will only matter if you make the site worthwhile and frequently used, so certainly that's the place to focus first. You have to have a popularity like google.com before misspellings start to matter for you. You should have plenty of warning before your site approaches that level. If you're buying more than 2 domain names in the early stages of your site, you're doing it wrong.
So I think the only place to really watch yourself is alternate spellings. Ideally you'll create a domain name that is unambiguous so that you don't need to consider alternate spellings at all. The more clear your choice, the better your pr will be, the better your seo will be anyway. If you must create a site like abearlygood.com, then you'll have to consider getting abarelygood.com as well, but better to avoid the problem to begin with.