Soapy situation

I'm trying to decide whether I should wash my baby's things with special baby detergent or just put her clothes in with ours. What do you do? My mom never used Dreft or anything like it, so I'm inclined not to, but my mother-in-law says regular detergent can cause allergies (or something like that, I don't remember specifics). Also, if I should use it, shouldn't I use it on all our shirts as well as her clothes? Her little face is going to spend an awful lot of time squished up against our shirts. :)