With the vast majority of U.S. workers planning to take time off this summer, the proliferation of cell phones, PDAs and laptops means most wont be able to leave their work behind for very long. A survey by Hudson, a professional staffing company, found that 23% of employees planned to check in with the office by phone or e-mail on most days while on vacation. That number rose to 38% for managers and 40% for entrepreneurs. With so many thinking about work instead of relaxing on the beach, its not surprising the survey showed that 34% return to the office feeling more stressed or just as stressed as when they left.