I bought the D3s near the end of it's production cycle - where the D4 came out four months later. I have no regrets as I could not afford the extra $1000 to get the D4. It was hard enough to get my husband to let me save the $5000 for the D3s. I'm lucky that he is willing to for me to get a pro body (upgrading from the D200) as he really likes the quality of photos I shoot.
So, in summary, the difference between the D4 and the D3s is not worth the extra $1000.