I've done it in two bathrooms and I like the result. Especially with a blue or a grey, I feel like it actually makes a small room feel bigger. Go for it!
If you decide you don't like it for some reason, it won't be very hard to repaint the ceiling. But I think you will like the result.
On flat ceilings, it looks great. On a textured ceiling, not so great. Our small bathroom has flat ceilings and has the walls and ceilings in the same shade of warm beige.
We've also done a lightened version of the wall color and a darker version of the wall color, and liked all of those more than a white ceiling. I think they all work better if the paint is more matte than glossy.
2 of bedrooms have this. One because it was easier with the windows, the other because I was lazy. I really like it because in the downstairs room, it heightens the ceiling and makes the room seem bigger and less dark (I did a light gray).
Rubes room is the other and I did some polka dot decals so it makes the room seem less choppy and cleaner on the whole.
Every room in my house has the ceiling painted the same color as the walls. It wasn't my decision--it was a builder's model home. I really like the look, but OTOH, my walls are pretty neutral. I think a light color would also be OK on the ceiling.