How long does it take to thank a donor?

How much time elapses between the arrival of a check and the departure of the thank mailmanyou letter?  I have heard many grand reasons for delays: the mail is delivered to a different building than the development office, thank you letters are done by a volunteer who only comes in once a week, the database makes it complicated, the finance department hogs the checks, the executive director wants to sign all the acknowledgements and sometimes they sit on her desk.  And on and on.  But the donor is not thinking about any of that.  Here is what the donor may be thinking:

 If you get the thank you letter out in less than 1 week – “Wow, this is an efficient organization that really noticed when I sent a check.  Maybe I will send a bigger one next time.”

If you get the thank you letter out in 1 to 2 weeks – “This is an organization with an average level of competence and donor appreciation.”

If it takes more than 2 weeks – “Did they get the check?  Do they care?  I should call, but I don’t want to call.  I know they are working hard, but I wish…”

What do your donors think about your thank you time line?