Thanks to the recent leak of Windows 10 build 9901, a number of consumer-orientated features have been revealed. Cortana, improved apps and many more things are amongst the many changes, however if you do plan on installing this leaked build, keep in mind that you'll have to jump through some hoops to upgrade to the next Windows Technical Preview build.
According to Gabe Aul on Twitter, updating to new builds on build 9901 is broken, meaning to upgrade you'll have to do it manually via an ISO or clean install fully. This could be a problem however, as Microsoft may not even release ISOs with their next preview drop.
@ZacB_; Yes, but not punitively. There is a bug in 9901 that breaks flighting, you'll need to upgrade through ISO.
— Gabriel Aul (@GabeAul) December 14, 2014
So, if you're planning to download 9901, make sure you keep that in mind. Windows Insiders who wish to give feedback on the update process may want to hold off on 9901.