The dust is used to merge two lesser level gemstones into a bigger one, and in making some special inventory bags IIRC. If you aren't into jewelry, it's probably not worth holding onto it.

The Auction House is operational, it's called Black Lion something, but as Anet says, you have a 50/50 of it not working. Keep trying and it will. It is currently not up 100% of the time due to extreme overloading.