A friend of ours used to vacuum all the time to get her baby to fall asleep. I vacuumed the other day and she fell asleep, BUT only while it's turned on. As soon as I turned it off she was awake.
So I tried playing vacuum noises on YouTube and it sorta worked. But again it only lasted 20 minutes because that's how long the recording was. But I knew I could do better. A quick google search found me an iPhone app that plays vacuum and other white noise for as long a you want for only $1.99! I bought it immediately.
So success? Sometimes it works and sometimes it doesn't. Its no miracle cure but in a crunch on the edge it will push towards sleep.
I use it at night when I can't get her to fall asleep and then this morning when she was up early to get her to sleep in her swing. I just put it right in there with her. This is the first time she slept in her swing (anything that's not my bed or my arms is a success to me, baby steps ok?). She slept for a little over an hour. She even woke up and went back to sleep by herself without someone holding her. I'll keep trying a little everyday until I can get her to sleep in her own bed.