Yep
Benefits of the Extreme over the Express:
a) better range (only helpful in large houses)
b) handle more wireless clients (only necessary in an office situation)
c) supports AirDisk (very useful think Time Machine)
d) more ethernet ports
The opposite:
a) smaller foot print
b) half the price
c) AirPlay support
I just had my four-year-old Extreme die, and I was planning on getting another one, but after I found out the Express has one up and one down ethernet port, I grabbed the Express (I have a headless mini we use as a media server, the rest are wireless clients) and haven't looked back.
Using Time Machine over the network is a little more of a hassle, as I have to mount a shared disk from the Mac Mini, but it's not something that's any more of a hassle than dedicating space on your desk and plugging into an HD whenever you want to back up.
The Express streams to my AppleTV, handles LAN backup and screen sharing just as well as the Extreme did. Range is negligible in my 800 sq ft apt, but the WiFi extends at least 100 feet from my front door.