I've subscribed to Loaddata.com for about ten years, and I've talked to the person who maintains the website and adds the data. She is very knowledgeable, and only adds tested data from known persons/sources. The data is collected from the manufacturers, both bullet and powder companies, with their permission. The other data is from the articles in Handloader and Rifle Magazines, and are referenced in the notes at the top of the page, giving you the issue of the magazine so you can reference the whole article and the information contained therein.
I find the site very useful, though it's not my only source for load data, but it's a quick reference and a fast way to crosscheck information. I'll never give up my printed manuals and annual supplements from the bullet/powder manufacturers, but Loaddata.com is a useful resource, in my opinion. There is also an extensive library of articles and research that is available to members only, with a portion of it available to anyone.
Hope this helps.
Fred