A very small bit of movement is normal with some milles, but much more and it's time to keep a closer eye on the pump (actually the bearings, but same difference). As our cars start to get up in mileage, it's good at every opportunity to spin the various pulleys (to listen for noisy bearings) and wiggle them like you did (to check for play / looseness).
Any ol' mechanic should be able to wiggle the fan and let you know if the pump has too much play, but generally everything should feel pretty tight when you wiggle the top of the fan lightly toward the front and back of the car. Sorry, I know that was pretty vague...so...generally the fan shouldn't move more than maybe a few millimeters. Hope this helps a little.
White 2007 Alpina B7
Supercharger clutch/bearings (check DIY), sunroof seal, quarterto8's 6000K angel eyes, bumper side mounts
Black 2002 BMW E66 / 745Li (sold)
KW v3's, blue angel eyes, 8000K headlights & HID fogs, rebuilt alternator, sunroof seal, CCVs, NGK Laser Platinum plugs, sway bar bushings, battery, timing & valve cover gaskets, valve stem seals, guibo joint, mechatronic sealing sleeve, trans fluid, alternator bracket mounting gasket, sanded headlights...