I hired a freelancer to build a conversation utility (http://blastr.me) ...a quick rundown on the site, it's basically to have organized conversations with groups. It's very, very simple. Instead of calling five friends and texting others to do something like go to the movies, you send one Blast and you can have a dialogue right there. Anyways, there are at least a couple things that are very slow with the site - dropping down responses (You click 'responses' on a Blast you're involved in) and it takes FOREVER, usually. Sending a Blast also takes a very long time. The site uses Facebook Connect, not sure if that could be a holdup. Any help would be greatly appreciated.
A lot of times, third party software/web apps/api's are unreliable - especially a Monster like FaceBook - that has so large of a user base and moving parts. I would only use Facebooks API to manage users/friends, otherwise make sure to be sending all emails, and anything else on your server. You can also try to get a dedicated host to speed things up... who is your host? Also, email sending isn't an instant thing - it takes time on the servers to process, ... but only a few seconds max. Also - DB might not be optimized - make sure your keys are in order.