The last couple of weeks have been both tiring and trying for us.
Tiring because we have been insanely busy with launching our Sanitation campaign  (Please help us spread the word about it ---> www.milaap.org/wtd) and trying because our servers on Rackspace (both production and staging) were behaving extremely slow.
This was really frustrating us - partly because our testing was hampered - but more importantly, all our initial set of users and evangelists were giving us feedback that the site is really slow.  Interestingly the page loading wasn't so bad. It was just that getting the first response from the server was taking time -- like 30secs  from the time you make the request to the first response from the server. Thats REALLY slow. Ideal load time should be sub of 3-4 secs.
Just as a control - we hosted a sample page on our office desktop ( which was also running Nginx, Mongo, Rails etc) and asked some of friends to test the speed and compare it to production. So are surprise and more frsutration, the office machine was serving requests much faster than the rackspace server for which we were paying moolah!
So we called up the RackSpace guys (they are famous for fanatical support!) but even that wasn't of much help - they told the regular random stuff - restart the server, check top and free memory etc. We did that; but it didn't change anything.
Finally, yesterday the BetterLabs guys (who also did the cloud server setup along with the initial web app development) did some changes and I'm really happy (and more relieved) that the website is fast now.  Load time is sub of 4 secs typically.
In the interest of open knowledge, here is what we did:
<tech stuff >
1. Added mod_expire and mod_deflate, mod_cache
2. Added indexes to MongoDB
3. replaced nginx to httpd+passenger
2. Added indexes to MongoDB
3. replaced nginx to httpd+passenger
</tech stuff>
I know - some of this stuff, we should have done right from the beginning. But yeah - we have done it now.
Do check out the site and let us know if you feel any slowness in the site loading.