Since BK changesets are ordered as a progression, you can also do a 
bsearch by clone trees to specific changesets, such as

bk changes -rv2.6.6..2.6.7 > /tmp/changes.txt
# view changes.txt, pick out cset 1.1587.39.1 as your "top of tree"
bk clone -r1.1587.39.1 vanilla-2.6 brad-test-2.6.6-bk
# compile and test the kernel in brad-test-2.6.6-bk

A couple of comments:
    - BK changesets are not a linear progression, they are in the form of
      a graph called a lattice.  Getting a path through there that you can
      do binary search on is not straightforward.

    - The CVS tree represents one such straight path, get just the ChangeSet
      file from the CVS tree and do an rlog on it - you are looking for the
      lines like:

      BKrev: 41316382Cxbyp1_yHDX8LmymGot3Ww

      That rev is the "md5key" of the BK rev and can be used anywhere a BK
      rev may be used (bk clone -r41316382Cxbyp1_yHDX8LmymGot3Ww ...)

    - The biggest time saver is knowing where to look for your bug.  If you
      knew that the bug was in drivers/scsi/libata-core.c then you could
      find each changeset which touched that file like so

      $ bk rset -lv2.6.6 | grep drivers/scsi/libata-core.c
      drivers/scsi/libata-core.c|1.39
      $ bk prs -hnd:I: -r1.39.. drivers/scsi/libata-core.c | while read rev
      do  bk r2c -r$rev drivers/scsi/libata-core.c
      done

      That will crunch away and spit out (in this case) 63 revs like

      1.1803.1.40
      1.1803.1.39
      1.1803.1.38
      ...

      and a binary search over those revs is likely to be fair more fruitful
      because the history of that one file is pretty linear.
-- 
---
Larry McVoy                lm at bitmover.com           http://www.bitkeeper.com