I'm working on adding support for different tempos and time signatures to my rhythm game. So far I've got the initial BPM being read, but not any tempo changes throughout the song.
It's been really fun so far because MIDI and SMF don't really seem to have any accessible C# libraries or quality documentation (that I've been able to find so far) so I've had to make everything from scraps of other people's code, technical documentation, and my own two braincells.