The practice is widespread, and with good reason.
Occasional personal communications (e-mail, phone, text messages) allow employees to take more control over their lives and their work.
With the proliferation of modern communication tools (cell phones, PDAs, laptops) come overlapping boundaries between work and personal life.
If work messages can intrude into evenings, weekends, and vacations, one can reasonably argue that an e-mail message to a spouse or family member can take place between 9:00 a.m. and 5:00 p.m.