Arduino I2C + SAA1064 7 segment Led Display Driver

I've just finished to interface an Arduino Diecimila with a board containing 2 SAA1064 and 6 LED 7 segment display trough I2C, it works perfectly without the pull-up resistor. The board was a leftover from an industrial scale. DataSheet available on the NXP semi website. Very easy to use , only one caveat , rebuild the wire library in any case , mine was broken. here is the site with the code and a photo of the board . http://sites.google.com/site/elettronicaarduinoesperimenti/Home/arduino-i2c-saa1064

it works perfectly without the pull-up resistor.

I assume you mean the I2C bus.

While it might work a look at the waveforms will show very poor signal shape. This severely erodes the noise margin and makes it more prone to interference and the maximum bus length is much reduced.

Yeah , sure , my reamark about the pull-ups was only for the experimenters , anyway looks like the Wire Lib engage the internal pull-ups in the atmega, anyone can confirm this and the real utility instead of real resitors on the bus ?

anyway looks like the Wire Lib engage the internal pull-ups in the atmega

Yes it does but they are not small enough pull ups to meet with the I2C specification.