UMPC: 4-7″ screen, generally touchscreen slate or convertible form factor, and usually attempting to squeeze a decent amount of computing power into that size (ex. Core Solo processor), thus usually making them fairly expensive (usually upwards of $1300). Examples: Samsung Q1 and Q1U series, OQO, HTC Shift, Fujitsu U810

Netbook: 7-10″ screen, mostly traditional clamshell designs (with a few “netvertibles,” with hopefully more to come in the future), the defining characteristic is an emphasis on cheaper, lower power-draw components (specifically, Intel Atom or Via Nano type processors) to fulfill the role of a “companion computer” (as opposed to someone’s main computer, which has more horsepower), thus keeping the cost relatively inexpensive (roughly $300-$600). Examples: Asus Eee PC’s, Acer Aspire One, MSI Wind.

Notebook: full size, traditional laptops and tablets, mostly in the 12-17″ screen range, and featuring sufficient horsepower to be someone’s primary computer. “Notebooks” have several subcategories, such as:

-Ultra-Portables: the simplest way to describe these is as “full power notebooks in netbook frames.” Essentially, they try to take the higher-end components needed to be one’s primary computer and squeeze them into smaller frames. Thus they typically have 7-10″ screens, Intel Core Solo or Core 2 Duo processors, and are typically fairly expensive ($1500+), so you pay a premium to get all that power in such a small package. Examples: Sony Vaio TX and TZ series, Fujitsu P1600 series.

-”Thin and Light”: As their name implies, these are essentially “normal” notebooks designed in such a way as to be thinner and/or lighter than the “average” notebook thickness/weight. Typically they have 12-14″ screens, are less than 5 pounds (“average” notebooks are 5-7 lb), are less than 1.5″ thick (with some examples being ultra-thin, like the Macbook Air or VooDoo Envy), and cost slightly more than “average” sized notebooks of similar power and screen size. Examples: Apple Macbooks, numerous business notebooks from HP, Dell, etc.

-Desktop Replacements: As their name implies, these notebooks are larger and more powerful than most notebooks, but aren’t intended for mobility. Typically they have 17″+ screens, weight ranging from 7-10 lb, and desktop-level components (desktop processors, high-end discreet GPUs (sometimes even SLI or Crossfire multi-GPU systems), and excessive amounts of hard drive and RAM). Typically fairly expensive due to their high-end components ($1700-3500+). Examples: HDX Dragon, most Alienware notebooks.

The classification of devices is becoming ridiculous, and is it so we know how to write about them in a uniform fashion?
Shouldn’t all computers “just get along”?