Hi Guys,
So I hate shelf bras probably as much as the person who started this thread. Here are my experiences:
1. You can take them to a tailor (I go to Silhouettes and Profiles in NYC, and they're the best), and they'll cut out the band and replace it with something less tight (like a loose elastic band. This isn't ideal for anyone who wants to completely remove the shelf bra, but for someone who just doesn't like how tight it is I would recommend this as an alternative to keep the dress as close to its original state. This method is probably least risky in terms of washing the dress and having it not come back deformed.
2. Cutting close to the seam. This works second best, although you do have to be careful about the seams coming apart (which will depend on how precise of a cutting job you do). If you cut too close, the seams may come apart. If you cut to far from the seam, the left over material will curl when you wash it, and if the tank top or whatever is tight, fitting, there will be a bump there.
3. Cutting along the sides of the shelf bra. I've used this method for the aforementioned dress. It works well if all you're looking for is some more give in the shelf bra. Cutting along both sides (not up the entire shelf bra, but just about an inch beyond the elastic) gives me enough give. If you cut it right, and just sew up the seams where you cut, this also is fine in the washer.