So technically, the correct usage of 得 for run very fast is 跑得很快 - why are there so many Baidu hits for 跑的很快 and 跑地很快?
The correct word to use in this context is indeed 得; however, because all three of these characters have the same pronunciation in Mandarin (de), they are very often confused by native speakers. This is similar to how some English speakers often confuse "there", "their", and "they're".

For more information on the grammatical differences among the three, refer to this previous question: 的-地-得, when do you use which?

[As an aside, while these three characters have the same pronunciation in Mandarin, they differ in other Chinese varieties such as Cantonese (的 dik、地 dei、得 dak), so this mistake does not occur as often with speakers of those topolects and replacing one with the other would end up sounding obviously wrong.]