To apply HTML formatting to uicontrol tooltips you may use a valid HTML string for the 'tooltipString' property of the uicontrol in MATLAB 7.2 (R2006a).
The following code creates a uicontrol with a tooltip which has line breaks and font formatting.
set(uicontrol,'tooltipString','<html><font color="black">testing</font><br><i><b><font color="red"><sup>123</sup></font></b></i>...</html>');
Please note that this is an unsupported feature and may change in future releases.
