This study claims that 11 percent of respondents under 25 and six percent of respondents over 25 would "check out a[n electronic] message" during "an intimate moment."
One in three respondents will take a message during a meal, and one in 14 during sex (this number jumps to one in 10 for those under 25). This may say as much about the quality of food and foreplay as it does the person interrupting them.
These numbers are backed by others. Intel did a study on the Internet and sex a few years ago, and Retrevo found a few months ago that Twitter may be the new poist-coital cigarette.