Wireless Data Transfer Capacity Limits

wireless data transfer has comparitively low data transfer rates than that of say fibrenodde( which goes inot GBps) . The main factors what I would see as affecting the speed of data transfer would be : modulation techinques being used like say OFDM and other LTE channel access techniques like , STDMA, CDMA 1x promise higher speeds, and also the band width allocation, for example UB where the band width is in the range of 7 Ghz as compared to 802.11's mere some MHz.
Keeping these aside, there are physical layer techniques like MIMO , SIMO which allow better data transfer as well , and then comes the positioning of the basestations and mobile stations .

EDIT: even the number of subscribers using the same channel effects 😛,

As with any other communication methods, the main limit is the channel capacity, which is proportional to the bandwidth and signal power to noise ratio.

If you can increase the signal power, you can have faster data rates to over come the channel noise. However, because most wireless communications operate in the microwave region, this is inadvisable unless you want to fry people in the area 😉 One can also increase bandwidth, but this might create cross interference if not allocated properly. So as Durga mentioned, modulation techniques are devised to increase the data rate as close to the theoretical channel capacity limits as possible, as well as smart usage of antennas.