FYI...WEP is actually Wired Equivalent Privacy.
Here's my thoughts on it:
Bad part about MAC Addresses is that they can be spoofed. My buddy Josh demonstrated a wireless router hack with his laptop and a MAC spoof script. The thing is that most routers will accept a connection to them as long as the MAC addy matches....which means that you could have as many connections as you want as long as the MAC is ok...kinda insecure if you ask me.
As far as encryption...even if you're using 128-bit WEP, part of the key is transmitted in plain-text. This is the initialization vector (IV) used in the hand-shake process. The IV is usually 24 bits, so the security of your WEP encryption is effectively 112 bits. I've seen people crack this encryption in about 8 days...Also, the WEP checksum is linear and predictable.
Did you know that there are readily available programs that can hack you WEP? I can think of three script kiddie programs that anyone can download and use piece of cake...some people have reported that in 3 days they can hack any high traffic WEP and in 7-11 days any low traffic one. To me, if my neighbor happens to be someone who can download a script and use it, then I'm going to be giving him or her free access and giving myself one heck of a headache.
Another point for those with small businesses. If you have a WEP network and then you terminate an employee...guess who still knows that key? Think that if they came across an add offering to buy a key they might sell? They're out there believe me. That ex-employee still knows the key and can sell it or sit outside your office with a laptop and sniff away all day long without you even knowing. That in itself is a reason I will never recommend wireless without lead walls.
Bottom line, I just don't think it is worth it. I can route cables through my walls no problem.
If you want ultimate secure WEP, you'll have to drop a few thousand on Cisco's switching key technology or else just wait until a new standard comes out that has more security.