Como outros afirmaram, a principal diferença é que um hub transmite pacotes de entrada em todas as outras portas:
A network hub is a fairly unsophisticated broadcast device. Hubs do not manage any of the traffic that comes through them, and any packet entering any port is regenerated and broadcast out on all other ports. Since every packet is being sent out through all other ports, packet collisions result—which greatly impedes the smooth flow of traffic.
O mesmo artigo da Wikipedia também sugere alguns usos para um hub:
For inserting a protocol analyzer into a network connection, a hub is an alternative to a network tap or port mirroring.
When a switch is accessible for end users to make connections, for example, in a conference room, an inexperienced or careless user (or saboteur) can bring down the network by connecting two ports together, causing a loop. This can be prevented by using a hub, where a loop will break other users on the hub, but not the rest of the network. This hazard can also be avoided by using switches that can detect and deal with loops, for example by implementing the spanning tree protocol.
A hub with a 10BASE2 port can be used to connect devices that only support 10BASE2 to a modern network. The same goes for linking in an old 10BASE5 network segment using an AUI port on a hub (individual devices that were intended for thicknet can be linked to modern Ethernet by using an AUI-10BASE-T transceiver).
Também há potenciais implicações de segurança, sugeridas acima. Se um hub for implantado, alguém com acesso a uma única máquina no hub poderá monitorar o tráfego para todas as outras máquinas no hub. Em geral, um switch não possui esse vetor de ataque.