Ever since Grace got her Dexcom G4, honestly, it has been spot on for her blood sugar readings. Oh sure, there are moments here and there - a 185 BG finger stick compared with a 150-ish Dexcom reading, but nothing earth-shattering in terms of being off. It really does stay pretty darn close to her actual BG via finger stick.
And the adhesive, for Grace, is really sticking. I use SkinTac just around the area where the adhesive will lie, but not over the spot where the insertion will happen. That thing sticks. Some edges come up here and there, and I just trim them off as they happen.
This current Dex is on Day #14 and still going strong.