What I would say is most important is the sense of web 2.0 politics - open source, ground up authorship, networked, distributed. So, the integration of the social softwares such as blogger, twitter, Facebook or Ning, de.li.ci.ous, Flickr, Hipcast (or moblogging, podcasting etc.), Google Maps are core to the concepts of the class. If your projects can integrate with any of these applications, you get extra points. If you are doing something outside, but can include a web element, a map, a feature of some kind, extra points. If you can work on the idea of a MIXED REALITY experience - either a mixture of physical and networked experience, or mixed through sensory scrambling, or spatial re-organization etc.
The most effective projects have created experiences that start in one condition and end in another condition. Walking somewhere, putting something(s) somewhere and leaving them there, and that combine several of these concepts into one overall experience.
The idea of permanence vs. mutability, the ephemeral quality of technology as public art.
The idea that art and creativity can collapse multiple meanings into one experience.
Having the public or the class create the content for the project. You create the structure for gathering that content, asking for it, soliciting it, provoking it, creating it.