I was sick of my iPhone not responding instantly to my finger taps the first time around (like when I had nothing loaded on my iPhone when I first got it) so I decided to figure out the issue. I felt that my iPhone had either reached its end-of-life or one of the programs was causing it to delay my touch response. I’m not ready to purchase a new iPhone 4, as the iPhone 5 is just around the corner, plus I got a brand new replacement just last week from the Apple store (cracked case — thanks Apple!). I closed all my programs, cleared all my safari history, cookies and cache, and still experienced the same issue.
I then worked my way to the one and only SPOTLIGHT settings (Settings > General > Spotlight Search) and unchecked all the options (Contacts-Messages).
My iPhone is now working normally. I am very happy, but of course the downfall is that your built-in search will not find anything. I will most likely go back and check a few options within the Spotlight settings, but I refuse to give up phone functionality for a search feature that I barely use in the first place. I hope this helps you just as much as it helped me.
You can read more about Spotlight HERE.