Look at the Twitter sign up page at <https://twitter.com/signup>

Even when you click on first input field "Full name" placeholder stays there until I start typing something. That is awesome.

Does anyone know of a good jQuery plugin that comes close to that?
['https://Stackoverflow.com/questions/7324767', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/796723/']
One possible problem could be that the web server is running out of memory and forcing the app pool to recycle. This would flush the InProc Session memory. You could try using Sql Session State instead and see if that resolves the problem. Try monitoring the web server processes and see if they're recycling quickly.
I would check the Performance tab in IIS to see whether a bandwidth threshold is set. 

1. Right click on website in IIS
2. Performance tab
3. Check "Bandwidth throttling" limit

If a treshold is set you might be hitting the maximum bandwidth (KB per second) limit. Either disable bandwidth throttling, or increase the limit.