1. Can current bootblocks boot kernel from level 1 ffs ?

This has been covered on current-users before.  Yes, they can and do.

      (I'm not going to convert my *extremely* stable FS's while seeing 
       fs-related panic reports on mailing lists, I still use 0.9 bootblocks)

1) That has very little to do with whether you're using the old or new
file system format.

2) There is a temporary change in the current sources that alleviates
those symptoms.  I'm working on a `correct' fix, but it's a pain.

3) `No pain, no gain.'

   2. I noticed that libgcc.a for NetBSD's gcc is much smaller than
      libgcc.a installed by stock gcc-2.6.0. (17KB vs 120KB).

The default GCC build includes some debugging info in libgcc.a that's
not really useful.  Also, 2.6 has a few new functions in there.

   Can our
   libgcc.a be used instead of original libgcc.a when linking object files
   generated by gcc-2.6.0 ?

`See above.'  Note that if you use 2.6.0 to compile NetBSD, you better
be sure that any bugs you report are not really compiler bugs, or you
will waste a lot of people's time!