Please note the article's publishing date. Some of the information presented below may not be current anymore.
With only a few critical issues left in the Drupal 8 queue and D8 being surprisingly usable, many developers already use it in small projects to play with the technology and to challenge themselves.
I have to admit, I am no exception - the embracement of many PHP technologies and (finally!) the jump to the OOP paradigm makes me want to stop writing right now and code some more.
Which projects qualify for Drupal 8 today?
I would wait a few months before creating bigger D8 projects for my clients. The community has to play some catching up first and port modules, themes and write documentation. On top of that, apart from all the OOP technologies we love, there have been some new drupalisms introduced and not documented yet - this combined with the lack of contributed module solutions makes D8 development much more time consuming for paid projects in comparison to D7.
Small projects however are very doable.
First however, it may be necessary to upgrade the server, as D8 introduces relatively high PHP and SQL requirements. See the official requirements page.