OK, thats seems doable. Downloading tiles for a large area and/or full zoom range means downloading many thousand separate tiles, which can be quite resource intensive. But it really shouldn't make the application totally unresponsive. I'll look what cane be done to fix this and also how to optimize the whole process, I also opened a ticked for this issue. Are you running your N900 overclocked ? That could explain the increased temperature during the quite CPU intensive tile download. Could you perhaps try to do the same batch download with normal kernel for comparison ?