In contemporary society, many people are overwhelmed by numerous tasks waiting to be done. Tasks are of a wide variety, ranging from daily tasks such as meetings at work to non-daily tasks such as buying groceries after work. To help remind ourselves of these tasks, common practices are to take notes on the paper-based day planners or Post-it and to use personal task manager software on computers and/or cell phones so as to take notes electronically. The latter, which is getting more and more popular in recent years, benefits by the trend of increasing penetration of smartphones. According to [1], in 2013, smartphone shipments will rise to account for more than half of all cell phones for the first time. Tablet PCs such as Apple iPad and Google Android-based tablets also boost the use of personal task management applications in our daily life.