Web 2.0 sites can be very beneficial for SEO. By creating high-quality content on web 2.0 sites, website owners can generate backlinks to their website, which can improve their search engine ranking. Additionally, web 2.0 sites are highly authoritative in the eyes of search engines, which can further improve a website's ranking. Furthermore, web 2.0 sites offer a way to diversify a website's backlink portfolio, which can reduce the risk of being penalized by search engines for an unnatural linking pattern. However, it's important to note that not all web 2.0 sites are created equal when it comes to SEO, so it's important to research each site to determine its authority and the type of links it offers.