Earlier this year, I spent quite a bit of time preparing river and water data from the National Hydrography Dataset for the main river in the area I grew up.
The more I worked and worked on cleaning up this data (and I did quite a bit), the more I really developed my take on imports and OSM. I started out only wanting to do the White River subbasin, as that is the area I grew up in and have good knowledge of.
Even then however I realized that if I were to import the entire dataset for even just one subbasin, I would be adding way more data than I could ever hope to actually verify or double check in the real world. Not only that, but I would have done nothing to increase the user base and OSM community in this area.
So despite the incredible amount of work I put in and the documentation I created, I really only ended up importing about half of the White River itself and the three main branches of it. I have also imported a few of the larger lakes and a couple streams which I have local knowledge of.
My opinion of imports at this point is that they are seriously harmful to the OSM community and OSM as a whole. I think the TIGER import was a seriously bad idea that OSM in the United States may never recover from.
For more on my import, check out the user page for my import user here