I only ask because that point is drawing near.
I recommend a novelty item in the vein of “I logged on to the Straight Dope message boards and all I got was this…”
They’ll be thrilled. 
Why 40,000? Maybe I could see 50,000 or 100,000. It’d be like the local furniture store that’s celebrating it’s 14th Anniversary.
Heh, good point. I just like numbers with a lot of 0s. Okay, then, how about the 50,000th?
pooped on!"
Member 40001 wins a free car, but 40000 gets nothing except my contempt.
Member 40,000 wins a copy of all of Cecil’s books, provided they send their credit card number, expiry date, and billing zip code to cecil@chicagoreader.com .
What? I didn’t say a free copy…yeesh
Jeebus! We just had User 10K!
Probably the same thing the 30,000th member won