iMini as a white noise generator helped this baby go to sleep!

via Paul Cunningham on The MATRIXSYNTH Lounge

Update via David in the comments: "New research indicates that use of white noise generators to help babies sleep may have long-term deleterious effects on hearing. The advise is: don't."

I did a quick search as I was curious if it had to do with the frequencies being played or volume levels and proximity of the device to the child. The following is via CNN and seem to be the consensus among other reports I found:

"But how loud should these machines be? How long should you keep them running? Should you put them close to your baby's ears, or on the other side of the room?

A new study in the journal Pediatrics suggests that some noise machines have the ability to produce sounds so loud that they exceed safe levels for adults, let alone infants, and therefore could potentially damage infants' hearing and hinder auditory development.

However, it's important to note that the goal of the study was to measure the maximum effective output levels -- not to observe direct effects on children. Experts disagree on what recommendations should be given on using these machines..."