One of my colleagues (rightly or wrongly) claims to have coined the term "cloud computing", and is an ardent proponent. It really scores when a very large requirement for computing is required for a limited period: today gives an excellent example with A level results coming out, and hence the UCAS website getting swamped. Temporary cloud computing capacity could have been hired to help with doing that job, giving plenty of capacity for the few hours of peak demand. OK the cost per hour would have been large, but a great deal less than buying permanent computers for the job, which would then stand mostly idle for the rest of the year.
From the farming, and most other, points of view, we increasingly need screens to see data, and keyboards and other devices to input that data. By the time you've packaged keyboard , screen and batteries, the extra cost of a central processor chip is small, and the "minimal terminal" would need memory for buffering in any case, and so you have a PC. You can fiddle around with it and call it an i-pad (or very often "That B****** thing!"...) but in the end it looks very much like a PC.
Computer professionals used to control the whole business of computer use, with much the same status as high priests. That has gone (thank goodness) but there is still a hankering amongst professionals to regain the power of the priesthood, and my nasty suspicious mind suggests that Cloud Computing may be an aspect of this. The fact that the computer cloud is not necessarily localised is irrelevant: someone somewhere still has control over the system.
Cloud computing DOES have some attractive features, and I'm sure it will grow to some extent in future years, but PCs and localised computing are enormously strong and robust in systems terms, and are, I think, well suited to the large majority of farming applications both now and for the foreseeable future.