i'll only buy online if i can get a better deal than in-store and it's something i've tried on and know i want.
for example, i saw a duvet that i really like at anthropologie, and i visit it every day on their website to see if it's gone on sale yet. when it does, i'll probably still order it through the store, though, and have them send it to me because the in-store sales are usually better. online shopping is usually research for me, i do the majority of my buying in person.
sometimes, though, online is necessary - i bought a sale jcrew dress online today because i wear a 14, and usually they only carry up to a 12 in dresses in-store.