When trying to find out why external hdd drives would sometimes be mounted, but not always, I found out that it only works consistently when you plug the N900 into the hub after switching on Vboost.

I am not sure if this was posted before, or if it is obvious to others, but I couldn't find it when searching the thread or the Wiki.

ps I use this hub, plus an adapter, it works well, can be powered by a 3mm Nokia charger, and is very compact.