I hope you aren't considering having Apache and MySQL running on the users machine? What a headache that would be to setup and keep running properly in a desktop environment.
Other than that this is a fine idea as long as you can manage the data properly with only a stateless connection. Think of 2 users trying to modify the same record at the same time, how would you handle this? I've found that PHP is a great language for serving up alot of database information, but when it comes to having an interactive database the stateless environment starts to loose its luster. I'm not saying that it can't be done (just look at the message board sites like this one) but if you will have users interacting with the same datasets it can get very sticky.