Well goodness gracious Jen, I've got the same GPS as you!
Overall, I'd say the Dakota 20 is a decent unit. If you've got the budget though, I would get the Oregon 450t or 550t which has terrain already pre-loaded into the unit and also has a bigger screen. Like Jen said, the screen is a bit small on the Dakota 20. Cabelas has them on sale right now for $200 which is a pretty good price.
As far as the mapping goes, for me it is usually a bit off. I live about 100 yards to the north of a major road and the unit would show me being just south of that road. I'd take it with me driving and it would show me being parallel to the road by maybe 100 yards or so. Ive bought 2 chips though from huntinggpsmaps.com and with those, it shows me dead on where I'm at. And with the private/public lands being shown, it works GREAT. Most of the chips are $100 per state and unless you go somewhere that is all public land, I wouldn't go without one. Hope that helps!