Switch – Layer 2 segmentation and network diameter

End-to-end is required because not ALL network layers are particularly reliable, and only the end systems know how much reliability is really required. Also, if there is more than one lossy link, only the end systems know which packets really need retransmitted (or corrected for) and end-to-end reliability therefore minimises the extra work to compensate for loss. And finally, all means for not losing packets take time. If every hop on a long path goes for near-perfect reliability, the overall latency will be enormous.

The end-to-end principle is what makes the internet practical.

I will complete Zoredache's answer.

A L2 switch does switching only. This means that it uses MAC addresses to switch the packets from a port to the destination port (and only the destination port). It therefore maintains a MAC address table so that it can remember which ports have which MAC address associated.

A L3 switch also does switching exactly like a L2 switch. The L3 means that it has an identity from the L3 layer. Practically this means that a L3 switch is capable of having IP addresses and doing routing. For intra-VLAN communication, it uses the MAC address table. For extra-VLAN communication, it uses the IP routing table.

This is simple but you could say "Hey but my Cisco 2960 is a L2 switch and it has a VLAN interface with an IP !". You are perfectly right but that VLAN interface cannot be used for IP routing since the switch does not maintain an IP routing table.