In the Baby Custer episode, Custer's house looks like the Stevens' house, but with a wall around the staircase to make it look different. did anyone else notice??

I'm sure you're right about that. Also, the Bellows had the same living room as the Stephens, while Larry and Louise Tate had Tony Nelson's kitchen. Another poster gave the www.harpiesbizarre.com link which details most of these crossovers between the sets of Bewitched and I Dream of Jeannie.

I thought I saw the paneling and amber windows of the Stevens' kitchen in some Jeannie episodes.....

Has anyone ever noticed that in the black and white episodes, the Kravitz's house is the same house that is used on "The Donna Reed Show" ?

Yep, the reason is because all of the houses used were on the same lot. You can see what each house was featured in by going to http://www.1164.com, and click on Warner Bros. Ranch.