The prevalence of adequate low-cost GPUs couldn't come at a better time. Both ATI and Nvidia have made it clear that they want to expand the roll of their graphics card from that of displaying graphics to a more general-purpose computing role. There is certainly reasons why this would be welcomed, as graphics cards are incredibly good at certain tasks. For example, Nvidia has been flaunting a program called Badaboom which can transcode video at speeds many times in excess of what a CPU can accomplish. There is a double benefit here, as well - the GPU can not only perform the task faster, it also leaves the CPU almost entirely free, which means that transcoding video does not result in a slow-down of normal computing tasks.
Such impressive performance is useful, but would be pointless if there aren't enough video cards around to run them on. But Nvidia is clearly not aiming Badaboom at high-end cards. Its own press about the program usually uses low-end cards like the 9800GTX and even the older 8800GT rather than the fastest, most expensive new cards. Considering the number of low-cost GPUs available, it seems that the attempt to transforms GPUs into GPGPUs could not come at a better time. However, while it seems certain that the use of GPUs for more general computing tasks will become prominent in the next five years, it is uncertain which avenue of advancement will be used. Nvidia has CUDA, ATI has Stream, and Intel wishes to break into the market with an x86 compatible graphics card, codnamed Larrabee. Open CL and the DirectX 11 compute shader also show promise.
While the trends towards cheaper GPUs and the rise of GPGPUs seem predictable and even certain, the speed of adoption is another matter altogether. Setting standards in the PC industry can be difficult, and there is little indication that the various players currently in or attempting to enter the market for GPUs have any intention to play nice. It is also not entirely clear if Nvidia, which still has a larger discrete graphics card market share than ATI, wants to allow the graphics card market to trend towards cheap, adequate GPUs.
It will ultimately be cooperation which determines how quickly the future arrives. If a standard for GPGPU use was agreed upon tomorrow then applications which use the potential of GPGPUs would become extremely prevalent in a short period of time. But there is an inherent disagreement between Intel and ATI/Nvidia, which makes the adoption of a standard unlikely. Anything except the adoption of x86 would be bad for Intel and the adoption of x86 would be bad for ATI and Nvidia. Someone will have to blink eventually, but this is one staring match which could last for a long, long time.