Got the same problem here- Radeon R9 290. Cursor appears comically large and low res. For me whenever my computer goes into sleep mode when I wake it up the cursor is normal sized again. Going into sleep must disable whatever faulty script in the AMD drivers is causing it.
Also for me, playing certain games enlarges the mouse again but problem is very intermittent. e.g. I play KSP and mouse is fine but I play Space Engineers and afterwards the cursor is big again.
Sidenote: ***** AMD and their *****drivers and customer support system, should have got a GTX 780 instead.
Intel i5 4670 3.4 GHz * ASUS Z87M-PLUS * Radeon R9 290 * Corsair RM850 * 1x8GB DDR3 Kingston RAM * WD Green 2TB * Windows 8.1 64 bit