The quick and intuitive means by which projects and jobs can be added, updated and moved around in schedules. It's a really handy way to both view and quickly update the full picture of workloads, schedules, availability and project progress.
While excellent for immediate-term planning, I would like to see a little more in the way of options for longer-term, or non-date-specific, planning - perhaps the ability to add a "pending" column that sits persistently alongside the day and date columns, to act as a reminder of jobs that will come onto schedule soon but aren't ready to be assigned to a particular day/week!
It would also be useful to be able to less evenly proportion time across days - e.g. spread a job over two days but assign more hours to one than the other, rather than the equal split as present.
These are feature requests rather than issues, though - on the whole the experience is excellent and does exactly as you'd hope/expect.
We have been trialling Float in order to replace a pen-and-whiteboard system in our office - it replicates the experience of that board almost exactly, with the added bonus that our team and other teams within the agency can view the schedule from anywhere, rather than needing to be at the office location. So far, with the exception of the minor suggested tweaks above, it has done everything we've needed it to.