I had my nipples pierced a week ago - both of them at the same time. It hurt like hell but after 48 hours it pretty much stopped hurting. I couldn't sleep on my front for three nights because any pressure and they did get quite sore. There sore at the moment if I wear a tight bra (I've resorted to wearing vest tops for a small amount of support without the pressure) or if I knock them.
You have to be careful you don't wear bracelets to bed because they may catch. The same for your partner if you have one (my boyfriend caught his bangle on it the other day and, yeah, that hurt).
The only other thing is seatbelts in cars tend to go across where the barbell will end so it may catch if you're not wearing a bra/padded bra but whatever underwear you have on it WILL rub. This is something to bare in mind - personally I don't find this too painful but it can make them sore if you're driving for a long time.
Major things to consider are; Firstly, can you deal with the pain of having it done? It is done by clamping the nipple and then pierced with a needle and the barbell pushed through after the needle was removed. I found that having the barbell put in hurt more than the actual piercing. Secondly, do you have a job where it may be a problem? IE do you work with young children or disabled children that have a tendancy to grab or fling themselves around. Thirdly, think about things like my previous seatbelt information, sleeping positions and any loose jewelry you wear.
I didn't think about these practicalities before I had it done, and I wish I had to make myself more prepared for how much care you have to give them, but I love them to pieces. Oh, and they do heighten sensation on the nipples but I don't have a problem with them rubbing against anything although it does look like your nipples are permanantly erect.
That's all the advice I can offer. Sorry for waffling!