One question I hear often from Windows 7 upgraders (more often than I would have expected, in fact) is, "What happened to the old network activity indicator?" It’s true: the Windows 7 designers got rid of that little icon in the notification area that flashes to indicate that your network adapter is busy. One of the key design goals of Windows 7 was to make Windows "less noisy," and the Windows design team paid especially close attention to pop-up messages and other potential distractions in the lower right corner of the screen.
Personally, I don’t miss that flashing icon. But if you want it back, you can download a tiny utility written by Igor Tolmachev. It’s called, not surprisingly, Network Activity Indicator for Windows 7:
It uses a mere 1.3 MB of RAM and does exactly what it promises.
Update: In response to a question via Twitter, yes, this works with 64-bit Windows 7 editions as well as 32-bit (x86).
Ed Bott 
There are also some nice gadgets available for Win7 that give more useful information about network activity. My favorite is the one from AddGadget.com (both wired and wireless versions) that graphs upload/download activity and shows related IP addresses.
I love this little gadget – I definitely recommend setting it to a lower ms like 60ms for the blinking lights if you want more to see more detailed activity