There are truths to both sides here. MicroB handles some stuff better than Opera does, but for the stuff that Opera does handle it mostly does it quicker than MicroB and with a smaller memory footprint. (MicroB seems to crash more as well, at least in the OS2007 version. For some of those cases it seems to be linked to running out of memory. So, memory and speed seems to be the main problem compared with Opera. Improved Ajax is the the major point MicroB has over Opera, presumably.)