Multiple Devices Tied to One Google Account

By the end of the year, I expect to own an Android tablet in addition to my DROID (or whatever I replace it with). I may or may not choose to pay for a data plan on the tablet - not sure yet. Will I be able to properly connect both devices to the same Google account? (In my case, a merged Apps account?) How will this affect the market and purchased apps? I understand that apps are tied to the Google account, but I assume I will somehow be required to purchase an app for each device?