I've observed my network usage over the past couple of days to see how much data I would transmit and receive over the course of a week while traveling. I've noted that there is a big difference between PC and mobile device use in terms of uplink/downlink ratio. With the PC, which I mostly use to access my eMail and for web based services, the ratio is about 10:1. The ratio on my N95, however, is close to 1:1 as I upload pictures, blog posts and eMails. Especially picture uploading with Shozu has a major impact on the ratio.
Other statistics say that 90% of the data traffic in mobile networks is from PC's and I think that also reflects my behavior. As a consequence, the uplink traffic generated by mobile devices is still an order of a magnitude smaller compared to overall downlink data traffic.
With faster uplink speeds becoming available the ratio could change once it becomes feasible to upload high quality video material from mobile devices in a reasonable time. That's about the only application I can imagine that could have a real impact on uplink use. Until then, however, the uplink will remain rather unused.