Roppongi, Shibuya, Harajuku

Hi,

I am in Tokyo for a 3 night stopover on the way back to London from Australia. I am keen to cram as much in as possible, do you think I would be able to see Shibuya, Harajuku and Roppongi in a day (I think we are staying in Roppongi)

This entirely depends on how much time you want to spend in each district. Some people need a full day others are done in 30 minutes. So, if you are one of those 30 minute people, you could squeeze even much more into a single day.

I would like to suggest that you check areas that aren't similar. For example Roppongi, Akihabara, Asakusa. Or, if you stay in Roppongi and will be able to check the stores in the evening (they open late) Harajuku, Shinjuku and Asakusa.
Unless you like to spend hours doing window shopping and actual shopping and must go in each store, it only takes 1 hr max. to see each area like Harajuku, Shibuya (my less favorite area) Ginza etc. this leave you ample time for other areas.

Thanks. The reason we want to see Shibuya is because of the busy crossing outside the station and the reason we want to see Harajuku is purely for the pop culture :-)

Hayley,
Ginza has a similar pedestrian crossing (4 directions plus diagonals) and is a more interesting area than Shibuya with very fancy stores. (Yurakucho on the loop line is the stop for Ginza avenue)
I like Harajuku but find the cosplayers on the bridge overrated. After all they buy their outfits in stores.. I do like the transition along Omotesando from youth culture near the bridge (and on Takeshita dori) to more and more luxury stores with fancy architecture as one nears Oyama. Try to find time for the Meiji shrine. You may see Shinto style weddings, another interesting glimpse at the culture.