According to TVCatchup's forum, the service will not work via Vodafone's 3G network, but we'd like hear from readers about performance on other mobile networks. The service works well over WiFi, and the difference between high quality and low quality is slight. The picture naturally looks less well defined due to compression in low quality, and the most noticeable difference is in the audio quality.
Not all of the UK Freeview channels are available, e.g. Virgin 1 and Quest are missing. TVCatchup has plans for premium packages in the near future, this could explain the omissions of some channels. However, a complication may be on the horizon for the free-to-air streaming service, as news broke this morning that ITV, Channel 4 and Five have filed a joint legal action against TVCatchup over streaming rights.
The streams come into S60 phones via the built-in Real Player, and therefore we can't take screen shots. Instead, here are two photos demonstrating the high and low quality streams.