As with any software, a new release often has bugs in it and it takes a couple of months to get it stabilized. In addition, it takes time for the Joomla website development community to upgrade existing extensions. There are over 6000 Joomla extensions! Granted, the most reputable and popular Joomla extensions do upgrade quickly, but this is software, and designers are only human, so mistakes always happen, bugs are always present, so it is wise to wait until the newly released version gets stabilized.
However, it is perfectly safe to upgrade to a new sub-version.
With all that said, my website design firm in Ottawa uses Joomla 1.5 version on our site, which we loaded with a layer of security, and it seems to be doing quite well, over three years already (touch wood). The reason we will have to upgrade to a new Joomla version is because of the extensions and components: soon it will be hard to find specialized components that support Joomla 1.5 .
In other words, if you have a good security layer installed on your site and if your hosting is reliable, you don't need to upgrade to every subsequent version of Joomla. Every 2-3 years should be sufficient. Just keep in mind that installing new components creates potentially a new security vulnerability. But if you don't plan on installing anything new after you've released the site, then staying with your version for 2-3 years, provided you have some additional security in place, like OSE Security component (get the pro option), for example, should work just fine for 85% of all websites.
If you need any help, contact me via this Ottawa Joomla blog or via my Ottawa website design company Joomla Bliss.
