From the amount of emails I have received from companies over the past few weeks pushing hosting space I believe we are seeing a glut of capacity currently in the market space. Interestingly not much of it is located within London which still struggles with power supply.
We are on the bandwagon as well but see it much more as a strategic addition to our connectivity offering rather than a standalone solution. Key points to note with any hosting is the long term commitment especially if your requirements change and you need more space or power. It seems most of the offers focus on rack space rather than power, which is good for the headline price but becomes expensive when you realise the power offered will only support a few servers rather than the rack you have paid for.
Another consideration is how well served the datacentre is for connectivity as a lot of these deals seem to be for sites in the middle of nowhere. Make sure that any hosting you do take is within easy reach of the sites you need to connect to and scalable for future needs.