I've been looking into incorporating with a partner, and we're both in different states, and obviously looking over Delaware's incorporation laws.
With incorporation, each state says that you need to file for registration within each state that you want to "do business in".
Does this "doing business" include having employed workers?
Does it include having a physical address?
Does it include accepting money from people from this state? (unlikely, but it could be interpreted that way)
Would incorporating in DE and registering in another state have any additional costs besides the registration fees for those other states? (such as income taxes, etc)
One would need to know which state you are considering, because each state has its own definition. For example, in CA (where I practice) the definition of "doing business" is "entering into repeated and successive transactions of its business in this state, other than interstate or foreign commerce". (This issue is discussed in "Doing Business in CA? Be Sure to Register ".)
An issue that you did not raise: Rather than incorporating in DE and registering in your two home states, you should consider incorporating in one state and registering in the other - you could save some money. Please see "Why (not) Incorporate in Delaware? ".
Disclaimer: This post does not constitute legal advice and does not establish an attorney-client relationship.
Not a CPA or attorney so before making a decision seek out appropriate councel.