Ubiquitous? pervasive? spime? - what's in a word?

What's the difference between 'ubiquitous computing' and 'pervasive computing'? Is there a difference? Does it matter?

I was reading an article on 'Effects of Pervasive Computing on Sustainable Development' ( >>> ) that began with the words 'Since pervasive computing is expected to become ubiquitous in the coming years ...' It set me off thinking about previous discussions of the differences between the terms, so I did a bit of Googling and Wikipedia'ing and came up with:

"Pervasive Computing" is: Shorthand for the strongly emerging trend toward:
* Numerous, casually accessible, often invisible computing devices
* Frequently mobile or imbedded in the environment
* Connected to an increasingly ubiquitous network structure
The aim is for easier computing, more available everywhere it's needed
(NIST Pervasive Computing Conference 2000 - http://www.nist.gov/pc2000/)

"Ubiquitous computing is a post-desktop model of human-computer interaction in which information processing has been thoroughly integrated into everyday objects and activities ... someone "using" ubiquitous computing engages many computational devices and systems simultaneously, in the course of ordinary activities, and may not necessarily even be aware that they are doing so.
(Wikipedia entry for 'Pervasive Computing' - http://en.wikipedia.org/wiki/Pervasive_Computing)

Dictionary definitions are not much more help:
ubiquitous - adj : being present everywhere at once;
pervasive - adj : spread throughout;

And finally - the IEEE Pervasive Computing Journal (www.computer.org/portal/site/pervasive//) describes itself as 'A catalyst for advancing research and practice in mobile and ubiquitous computing' (sic).

So, they seem to be somewhat interchangeable.

And 'spime'? - that's a word made up by writer Bruce Sterling for a "currently-theoretical object that can be tracked through space and time throughout the lifetime of the object ... spimes as coming through the convergence of six emerging technologies, related to both the manufacturing process for consumer goods, and through identification and location technologies.

These six facets of spimes are:
1. Small, inexpensive means of remotely and uniquely identifying objects over short ranges; in other words, radio-frequency identification.
2. A mechanism to precisely locate something on Earth, such as a global-positioning system.
3. A way to mine large amounts of data for things that match some given criteria, like internet search engines.
4. Tools to virtually construct nearly any kind of object; computer-aided design.
5. Ways to rapidly prototype virtual objects into real ones. Sophisticated, automated fabrication of a specification for an object, through “three-dimensional printers.”
6. “Cradle-to-cradle” life-spans for objects. Cheap, effective recycling.
(http://en.wikipedia.org/wiki/Spime)

Ubiquitous (or pervasive?) computing could be a way for spimes to be developed and used - it would be interesting to think about potential health applications.