There's an interesting comment on the new Bulgarian flat tax at Novinite, which is a Sofia based news agency. It says:
Certainly, [flt tax] has a fair number of supporters and detractors, but even the staunchest advocate of flat tax will agree that it is not a magic wand that will solve all the problems in an economy.
If properly applied, flat tax could go a long way to achieve that goal, but no matter how low you push the taxation rate, it will not attract too many new investors if it is not coupled with measures to fight corruption.
Part of the reason why the flat tax has been an efficient tool in diminishing the "grey economy" in other countries was the willingness of governments to couple it with draconic measures to crack down on tax evasion.
Even though it is a long-term goal, this kind of measures give the foreign companies the feel that things are going in the right direction and makes them more likely to invest their money in those economies.
Bulgaria, on the other hand, has notoriously been sluggish with its fight against corruption and the organised crime.
If the cabinet fails to supplement the flat tax with a package of measures that would make corruption and tax evasion economically unsound, it will only achieve the further erosion of the macroeconomic stability built up by previous governments for the suspect goal of winning another election.