HUD stats aren't great for reads period. Looking at hands opponents have shown down and reviewing their lines is much better.

But since most of us multi-table, sometimes all we have are HUD stats. I start taking pre-flop stats (VPIP & PFR%) seriously around 100 hands. But if someone's 80/25 over 40 hands, I still take that into account. With post-flop stats (Aggression, c-bet %, folds to c-bet %, WTSD%) I like to have 500+ hands. I basically ignore these stats with less than 200 hands and start considering them between 200-500.

These are rough guidelines off the top of my head, ymmv. An eye-opener is to look at how your stats vary from session to session. I find that in 100-200 hand sessions my pre-flop stats can vary a lot... VPIP 16-26, PFR 6-15... and post-flop stats even more.