Currently, resuming from pause automatically adds in a 20ms delay into the music. This "20ms" value is based off of personal experimentation in figuring out what works best (aka still smooth resume but constant pause/resume doesn't go backwards in the song). If there is enough request for it, I guess I can make this value an adjustable setting, but it seems a fair number at the moment and avoids the possibility of cheating.
That said, however, this only works for MP3s. Due to the same .ogg bug that causes timing issues for .ogg playback (see
http://code.google.com/p/android/issues/detail?id=11590 ), pause-resuming of .ogg music playback is inaccurate and will jump around some. Best workaround right now is to re-encode your music files as .mp3s.
As for the slow downs/stops, no Beats doesn't have them implemented at the moment nor do we plan to by design (or rather, laziness as adding them would involve completely rewriting the entire notes displaying engine). When the BPM is lower at some parts of the song, the notes are just more spread out. When there are stops, there are just gaps in the notes. Imagine that you are always playing at a constant speed modifier, such as StepMania 3.9's C400.
~Keripo