leofs PMed me about my toastedBoot bootloader http://code.google.com/p/toastedboot/
which is basically adaboot++. I mostly put it up on google code because there was no other home for modded bootloaders -- they were just zip files on people's web sites, which made it hard to find the "latest".
One adaboot feature is that it goes direct to the sketch on powerup and only waits listening to the serial on reset. That seemed to satisfy him which may be why we haven't heard anything more.
BTW, features I added to adaboot are:
1. if you double click the reset button, it waits a LOOONG time for a serial. This is very useful when your board is far away from the computer and you don't have the auto-reset feature (i.e. using a FTDI cable). Originally, I had it set up the opposite -- it would wait a long time by default, a double click would drop direct to the sketch. Unfortunately, the auto-reset feature of the standard Arduino actually resets the board more than once so I swapped it so toastedBoot would work on boards that support autoreset. But if you are using a clone you may prefer this other double-click behavior.
2. The pin 13 led fades in and out while the board is waiting for a sketch. This way you know it hasn't hung somewhere.
3. Code crunching -- I reworked the code a lot to make it smaller so that new features could be added in the same flash space.
On a slightly different topic:
I think that it would be possible to write a sketch that updated the bootloader. I mean why not? Its just writing to flash. The problem with this idea is that if the sketch was interrupted mid-write your board would be bricked -- you'd have to buy a $20 ICSP to recover it. So maybe its not worth the support calls it would generate. What do you think?