It's not the norm, but if it works for you, why not?
I see it a lot in shared kid's baths, where the 'private' functions are split from the sinks.

In a master bath, I could see it being a problem if one of you wanted to shower while the other was using the toilet, but otherwise, I kind of like the idea. The rest of your bath could be decorated very attractively if you didn't have to consider water-splashing quite as much.

That's exactly what we have. I designed the house and did NOT want the shower in the vanity area. We have a doorless walk in shower, and having it in a separate room really keeps the warmth in there. Another plus is that our mirrors don't get fogged up. If you have kids it is great having the shower in a separate room is a definite advantage. I have always had a vanity area outside of the shower area, and my kids were always available to me while I was brushing my teeth, putting on make-up or doing my hair. If my husband was showering in that same area I wouldn't have been as accessible to them. Here's a pic of our layout:

I forgot to mention that the issue of one of us needing to use the toilet while the other is in the shower is not a problem at all because we have another bathroom nearby on the same floor. Also, because of the way that the room is set up, someone could use the toilet without being seen by the the person in the shower.

We have a tub/shower combo and toilet in a separate room from the vanity and I wouldn't have it any other way! I can't think of a single downside. Ours currently has a regular door and I'd really like to change it to a pocket door, but that's the only change I'd make.

My mother's apartment is very much like terriks' layout, but much smaller. It actually works very well. However, do look into the pocket door if you're going to do it.

Ditto on what Terriks said.

I have a large vanity area with two sinks and a tub, and the shower stall and toilet are behind a separate pocket door. The vanity area never gets heated or fogged up. It's ideal and I cold never figure out why they didn't design more homes like this.

I should tell you that we changed the door to a pocket door during construction.

I'm doing it in a guest bath that won't see much use, except over the holidays and the like.

The toilet/shower area is separated from the vanity/tub area by a pocket door. The tub also has a shower.

My thought was that the visiting relatives with small kids could use the space as families, sort of: dad could be in the shower area while mom did her makeup at the vanities and the kiddies bathed in the tub. Or, two people could shower at once, so long as the one in the tub area isn't too sensitive.

Not a perfect solution in many ways, but all it required in my case was adding a pocket door between the shower and vanity area, and it should allow guests a few more options.

Thanks everyone! The main first floor bathroom (which is also the kids' bathroom) will be like what everyone else has described (tub/shower and toilet separated by a door from the vanity area).

In the master, the shower and toilet will be separated from the TUB and vanity area. Here's the floor plan if you wish to look.

My sister's masterbath is set up that way and I love it. I didn't think to have mine done that way or I would have considered. No steamed up mirrors and no drooping hair if you are doing your hair and hubby is showering.