This type of question (CMS vs Custom) precedes Wordpress and ultimately is all about the specifics of the site you are building. Wordpress is most likely the best current option for any site that you want to build using a CMS. But there are still many cases in which you won't want to use a CMS or feel that the site/system you need has to be designed and built from the ground up.
Even if you do choose to use Wordpress (or any other CMS) to build your site(s), it is still important to not let that be a crutch. Make sure you still advance your knowledge and skills of web development and use that to improve any site you build on Wordpress (or any other CMS). However, when you do use a CMS you'll be putting your site in a box. It's not impossible to get out, as there are plenty of plugins available for most CMSs and you can generally modify the code directly for specific cases, but typically when you need very specific custom solutions it will be easier to build when you are not contained within any sort of framework (CMS). Simply because you aren't building a mod or plugin for the CMS but instead are building a solution/system for your own site.
But again, it's an age old question that always depends on the specific cases of each site you build. Most sites can probably be built on Wordpress with little effort, but there will still be more complex sites and cases where you'll be better off building it outside of a CMS.