If you’re using iPhone 4 or iPhone 4s on iOS 5 or iOS 5.0.1 your device might have strange Spotlight Search problem… No matter if your iPhone is brand new, unjailbroken or jailbroken…
Either Spotlight Search is not responding at all, or it is working intermittently – sometimes it does the search instantaneously as it is supposed to be, and the other time it takes minutes to display results.
Strange thing is that people who contacted technical support got answer that Apple stuff is not familiar with the problem.
And yes – there’s a temporary solution until the Apple fixes this in some of the next iOS updates.
The solution is to disable searching your mail.
Just go to the Settings > General > Spotlight Search and uncheck Mail.
Here’s a YouTube video that illustrates the problem (and the solution).
If someone found out better solution, please do not hesitate to post it as a comment.