In a a new tutorial posted on his blog Martin Sik shows you how to "steal" the "did you mean..." functionality that Google's sites currently offer. His example uses cURL to get the current Google request URLs and fetch the associated results.

I really like Google and the classic "did you mean" feature is really great, unfortunately when I wanted to implement it into my project a realized that it's not provided by any of Google's APIs. [...] I believe for most developers [having a large dictionary and extend the dictionary when new terms are available] are unachievable. And so it's for me. So I was thinking if I can bypass these drawbacks and let Google do all the job for me.

The source code is included with the post showing two methods - fetching a "did you mean" block to parse or how a term is attached to a Google URL and the results are returned in JSON and parsed for display. Obviously, this is an external dependency you could consider if you put it into your application, but it can be quite a powerful tool in the right situations.