Some have mentioned this for Windows RT, but I'll point out that sharing paid apps works on full Windows 8 as well.

I have shared purchased apps between my wife's profile/account and my own profile/account. Simply go to Store/settings/account and sign in with the other Microsoft account. Then look up "my apps" and re-install whatever paid apps you want. When you are done, simply go Store/settings/account and click "sign in with a different account" and it will automatically sign you back into your own regular Microsoft account.

Pretty sweet that they allow multiple Microsoft accounts to sign into the store on a single Windows profile.