How many laptops to a wireless AP?

[Ted Roche]

I'm looking at setting up a caf/é/-style space where somewhere between 
10 and 25 people will be working on their laptop. I'd be bringing in an 
internet connection, likely a Comcast 16/2, and I anticipate most folks 
will be surfing with 802-11g or n (draft). Mostly surfing, with 
occasional file uploads, YouTube viral videos. Twittering, or debugging 
a misbehaving Drupal app.

Can 25 people share a single wireless access point, or will more than 
one be needed? Would a consumer-grade WRT54G or equivalent be suitable? 
For simplification, let's assume an open 40' x 50' space with fairly 
clear line-of-sight and no major physical obstacles. I recognize if 
there's a second space behind a brick wall they'll likely need their own 
WAP or a switched connection. I'm more concerned with the load on a 
single WAP. I've done mostly wired deployments or single AP layouts with 
a couple people, so I'm not sure where the loading will drag it down.

Any insights on things to set up (DDWRT, traffic shaping) or avoid would 
be appreciated.