It seems to be a big question in the community whether to develop new web sites using Drupal 5 or Drupal 6.
For this site I am using Drupal 6, and I am yet to encounter any problems. This is mainly due to the very few modules I use. Most of them are core apart from Google Analytics, Tagadelic and the collection of image solutions I have been trialing my way through until I find one that it better than writing the HTML.
When I first encountered Drupal at the start of this year I was set the task of building http://communitytheme.ibo.org the basic site had been started in Drupal 5 and I helped finish it. There seemed to be loads of modules used such as CCK, Views, Panels, Image Field, Embedded media field etc. Within weeks of the site being released Drupal 6 came out and there was no chance of moving it over because of the module support, and even now there are many modules that have still not been released.
Although using the experience I have gained since I would say many of the modules used were not needed and the site could easily be developed using Drupal 6 now with a little planning.
I am now working on all new sites in Drupal 6 and when going back to Drupal 5 it strikes me as feeling so out of date. There is one site that I am currently developing in Drupal 5 because of Panels, the customer wanted three main content sections on the home page and my first thought was Panels, but now I am starting to question that. If I set up the regions in the theme I can just create views as blocks and hey presto, no need for panels.
So in summary, I think all new developments should be done in Drupal 6, and if you can't why not? there must be a way around it!