Great question. I have around 100 songs from different genres: dance, alternative, easy listening, pop and spiritual/chill out. It varies, and I can adjust due to my mood. Speaking of which, I am currently listening to Moby right now. The playlist on iTunes on my laptop is completely different to what is on my iPhone 5. Mix it up, love it.
I uploaded my entire CD collection onto my computer and had it as all one big playlist. It culminated in about two days worth of songs if played continuously. The songs ended up taking too much memory on my computer, so I ended up deleting them all. I only listen to music on my CD player now.
I have about 1000 songs from old to new.But my favorite playlist is called Gym .I add just about any fast track in this playlist to listen to it while i am working out as it helps me walk faster on the thread mill. I also use it in most parties to play this list while friends are gathered.Its very handy