I have not read about any problems with the tankbag magnets being strong enough to affect the HD in the notebook PC. And that's about the only thing that the magnets would bother. Plus the magnets usually drape down the tank, not under the bag where the notebook would be. If you really want to use the tankbag, put a magazine or portfolio pad & paperwork under it as a buffer.
However...I have read that the vibrations in a tankbag are hard on the notebook, and the mags all promote the use of a backpack/courier bag. Again, the additional padding/paperwork would be helpful.
I have a gummit-issued notebook too, and when I take it home, I put it in my courier bag, but I prefer to use that for commuting anyway. I have duplicate power supply at home, so I don't have to carry all that back and forth.
And make sure you back your data up to the LAN so if you do lose the notebook or the vibrations get to it, you're not screwed!