I put in a 8GB Mushkin ram kit a week ago, recognized on first boot, no problems at all so far. This kit's specifications said it was Apple compatible, several other iMac & Mini owners reported it was good, and it cost about $40 similar to other brands. I know other chips are Apple compatible but this reduced the possibility of hassles requiring me to return the chips.
The outer stick required a little more care to get inserted properly.
I notice the ram temperature is a little higher at 40C than the original 2GB at 30C or so, interesting difference but not a problem.
I'm not doing anything heavy with this base Mini so there is usually not a noticeable difference in the speed of 8GB over 2GB, but the occasional paging delays are gone and now I don't need to worry about programs using too much memory. One thing I notice is scrolling up/down long web pages in Safari is smoother with 8GB, probably because more Ram reserved for video memory, 512MB vs 288MB.