The purpose of this study is to investigate Web 2.0 awareness of preservice teachers by determining their innovation-decision process of Web 2.0 technologies. In this context it is aimed to obtain findings related web 2.0 adoption processes by determining which of the technologies are at the beginning or end of their diffusion process among the preservice teachers. Considering Web 2.0 as an innovation, the research is based on Diffusion of Innovation Theory [ 12] and especially on the time element of this theory. " No awareness", " knowledge", " implementation" and " confirmation" stages are handled as innovation-decision process stages. Web 2.0 awareness of preservice teachers is investigated within a longitudinal perspective. The study is a descriptive study designed as a longitudinal panel type. The study group comprised of 140 students (73.5% female, 26.5% male) studying at teacher education programs of a public university. The data were collected in two phases in the year 2009 and 2011 from the same preservice teachers. Data has been collected by Innovation-Decision Process Questionnaire developed by the researchers. Innovation-Decision Process Questionnaire aims to determine the innovation decision process of Web 2.0 technologies and consists of social networks, learning management systems, search engines, blogs, podcasts and wikis as Web 2.0 technologies. As observed from the study; the diffusion of an innovation differs according to each technology. Within two years; the awareness of preservice teachers in all Web 2.0 technologies are increased. The results have revealed out that the diffusion process of social networks, search engines and blogs are nearly completed; for learning management systems and wikis, the critical mass has been exceeded. Unlike the other technologies, it is observed that the diffusion of podcast is progressing slowly but has not reached the critical mass yet. Thus Web 2.0 technologies have positive effects on learning and interaction. Future studies in educational context could determine the advantages and disadvantages of slow diffusing technologies.