Netbooks: Swivel Touchscreen Does Not Equal Tablet PC (the source of the picture) correctly explains that a netbook having a touchscreen does not make it a Tablet PC. In other words, just because you can touch doesn’t necessarily mean you can ink, very well anyway.
Having a tablet-enabled OS (XP Tablet PC edition, Vista, Windows 7) is not enough. Passive digitizers that are “soft” make touch navigation easy but interpret your hand or palm as an intended touch. The result is while inking, touching your hand or palm to the screen is (incorrectly) interpreted as a pen stroke, with none too readable results.
“Hard” digitizers avoid this problem but are not very touch-friendly. My Fujitsu P1620 is like this. Touch navigation with my fingertips is difficult. I often have to use my fingernail to emulate a stylus.
Of course, there are and will be netbooks that support inking as well as touch. However, they likely will be on the expensive side. The moral of the story is don’t assume that you can ink well on a touchscreen.