WEB2.0 (proper WEB2 - not "guestbook" WEB2) do not need categories.
If you are used to using the sort of service which offers "500 WEB2.0 accounts for $10" then you might be used to seeing categories used. But these sites are just glorified guestbooks and if the definition of WEB2.0 were ever actually set in stone (it's not - it's a very loose definition) then most of these junk sites hosted in eastern Europe or the far east would not meet the criteria, they certainly are nothing like Wordpress.com or Hubpages or Tumblr or whatever, they are basically junk.
The good WEB2 sites that Ultimate Demon supports rarely require categories. But you need to define subdomain (that will form part of the URL - so no spaces) title and subtitle AND tags. That's enough category for anyone
You can post full articles, use the accounts and URL for more than one article, embed photos (and is some cases video and even podcasts and stuff on some of them)
I have about 255 that I can create accounts on (inluding ELGG and JCOW platforms) and about 105 that allow full submissions (multiple submissions etc) PR ranges from 9 for wordpress to quite a few zero's for the domain URL, plenty in the middle around 3,4 and 5 - a nice mix. Many have a LOT of traffic, so posting good content gets you a lot of direct visits...always nice!
Scritty
[EDIT - SPELLING - AGAIN]