The early days of Facebook chat where god awful, with tons of missed messages and things not syncing within the web and 3rd party clients. AIM (and even Yahoo and MSN) were over a decade ahead of that garbage before FB eventually caught up with having a messaging system that didn't suck ass.

In fact most things Facebook did originally it did poorly: poor quality photo storage (Flickr offered high quality or even original quality for a fee), garbage messaging, etc. It eventually caught up after it got big, because everyone was already using it .. and all the other platforms lost market share or became niche.