Hello.
I`ve upgraded most of my network devices to 6.35.2. I think it was very idea at the end. Part of those devices worked quite well on 5.25 (like RB750UP). Other on 6.27 was working properly too.
Anyway I see that current sofftware puts a lot more "stress" on CPU each of the device. I run auto configuration backup script 2-3 times a week, and every time It runs (in the night) i see lots of alarms in nagios logs, like high ping, lost packets and the worst thing is... that devices disconnects, just like that (during export), And don`t tell me its because device is overloaded... Yes its overloaded by something during export, that puts a lot o stress on cpu, its not high traffic case, because in those places after midnight only arps "fly"  if you use /export command for example on RB750UP its gonna export just half of config and besides it takes eternity (simple config with 4 ports bridged and export "hangs") Isin`t something wrong here? I`heven`t seen such behavioer before...

Not only you see this. But mikrotik still believe that it doesn't matter. You can find this topic already discussed here.

I do notice that /export takes a long time on slow devices like RB750, but the same thing is usually true on other manufacturer's routers (e.g. Cisco).

What I have not yet noticed is that it causes operational effects like lost or delayed packets, or that the export would fail or be incomplete.

I cant` find anything related export issues   Could you give me direct link? Anyway, this problems make me so mad Do downgrade will help in this situation?

I do not understand you cannot find relevant threads. The first link I got from google was this:
http://forum.mikrotik.com/viewtopic.php?f=2&t=105498

How it is possible the people cannot spend 5 seconds on google, but rather spending many minutes writing "new" things again and again?