Well, being the anal retentive person I am, I actually researched this out. Turns out you can't just randomly jumble the middle letters, there's a bunch of things which can make it easier or harder. Example:
1) A vheclie epxledod at a plocie cehckipont near the UN haduqertares in Bagahdd on Mnoday kilinlg the bmober and an Irqai polcie offceir

2) Big ccunoil tax ineesacrs tihs yaer hvae seezueqd the inmcoes of mnay pneosenirs

3) A dootcr has aimttded the magltheuansr of a tageene ceacnr pintaet who deid aetfr a hatospil durg blendur

If you were like me, the sentences got progressively harder. (actually, I found 3 easier than 2)

Anyway, I still thought it was fun so I wrote a small Visual Basic program to jumble the words, don't be surprised to see some weird text in here ^^

Trehe is no Good, Trehe is no Eivl, Trehe is olny Precepsvite.