You need to pay attention to how many amps your Hub can produce.
I have a 10 port Hub that is only 2.5amps therefore I can only successfully mine error free with 5 USB Miners. Since this hub has 5 useless ports for mining I'm returning when the DLink's I ordered get here.
There are several DLINK 7 port hubs out there and each will support different amount of miners.
1) the DUB-H7/B will only support 4 as it is rated at 2.4 amps.
2) the BUBH7A A5 will also only support 4 as it is rated at 2 amps.
3) the EUBH7EB HW Ver. B1 should support 6 as it is rated at 3 amps.
There is only a handful of HUBS out there that will natively support 7 USB Miners and are rated at 3.5 amps.
1) Delock's B/N87467 rated at 3.5 amps
2) Cyerpower High-Speed Hub CP-H720P, rated at 3.6 amps
3 Belkin Hi-Sped USB 2.0 7port Hub F5U237 is rated for 3.8 amps so should handle 7.
There's a couple more on this list that are 7 ports and at least 3 amps on this list.
http://elinux.org/RPi_Powered_USB_HubsThere could be others as well not on this list.
They key is the rating of the Power the hub can handle. You must have .5 amps per port on the HUB to properly run your miners.
Some people have hacked their USB Hubs to actually get .5 amps to each port. Usually ending up with some melting
some however don't.
The DLINK above that should be able to 6 seems like a good one as it leaves one port open to daisy chain the next hub.