Personally, I love it when I see people or commercials on radio or TV tell others to "Google X" to find out services. Yea, it is a bit risky - what if you do not rank well or your ad is removed? But it is cool.
One advertiser said in a Google AdWords Help thread, am I "allowed to ask customers to "google: keyword"?" He wants to know if Google would sue him for using the word "Google" in a campaign for telling customers to Google him?
I doubt it but a Google AdWords representative said it is better to be safe than sorry. Instead she/he suggested "it would be far better to say 'Do a Google search for keyword" than to say Google: keyword."
Legally, maybe but it has less appeal to it, in my opinion.
Plus, I doubt Google has an issue with it.
I find it funny that Google chimed in on this topic, to be honest.
Forum discussion at Google AdWords Help.