This is the addition I made to the boards.txt file.
###########################################################################
attiny25at8.name=ATtiny25 @ 8 MHz
# The following DO work (pick one)...
attiny25at8.upload.using=arduino:arduinoisp
attiny25at8.upload.maximum_size=2048
#attiny25at8.upload.speed=19200
# Default clock (slowly rising power; long delay to clock; 8 MHz internal)
# Int. RC Osc. 8 MHz; Start-up time PWRDWN/RESET: 6 CK/14 CK + 64 ms; [CKSEL=0010 SUT=10]; default value
# Brown-out detection disabled; [BODLEVEL=111]
# Preserve EEPROM memory through the Chip Erase cycle; [EESAVE=0]
attiny25at8.bootloader.low_fuses=0xE2
attiny25at8.bootloader.high_fuses=0xD7
attiny25at8.bootloader.extended_fuses=0xFF
attiny25at8.bootloader.path=empty
attiny25at8.bootloader.file=empty45at8.hex
attiny25at8.bootloader.unlock_bits=0xFF
attiny25at8.bootloader.lock_bits=0xFF
attiny25at8.build.mcu=attiny25
attiny25at8.build.f_cpu=8000000L
attiny25at8.build.core=tiny
###########################################################################
It would be easy enough to also include make a 1mHz section.
I had no issues with any of the library functions that I listed above.
I will check out the Tiny Debug Serial. Sounds like a great addition.