We've done a few jams before, although we normally participate in 72-hour jams (notably LD Jam). The hardest part for us was probably cutting out 24 hours of work and focussing down on a smaller feature set. We decided that we'd borrow ideas from an existing game since we didn't want to spend too much time planning actual gameplay, and instead wanted to get working on features.
Fortunately we're a team of 4 so we can split tasks quite nicely. I have background in Computer Science, so I took programming and music. The other members are experienced in Architecture and Film Production, so we're quite geared towards this.
Overall, it's been quite an interesting experience, and we'll definitely be doing it again next year (if they host one).