Alex, have you employed these rules yet? I like them and am planning to go with them but was wondering whether you'd any lessons from experience with them yet.
I will be testing them in an upcoming campaign! I'll keep you posted.
For what it's worth, I've been using the flat thief numbers from the first post for a couple of months, and nothing's broken yet. No gear options in use, and no assigning difficulty modifiers; the numbers are what they are, which makes it easy for me. The thief's 3rd level, eyeing 4th (with attendance we have a spread from 4th to 1st level PCs), and the only difference I've noticed from stock D&D is an actual shot at finding and removing traps. No-one's complaining about the thief overshadowing them, or wishing they had one over their existing character.
Hijinks haven't come up much except for listening for rumors, and so far my plan is to use the old progression for those.