Why not enable font lock by default?

[Jason Spiro]

Ville Skyttä <scop <at> xemacs.org> writes:
> On Friday 06 July 2007, Jason Spiro wrote:
> > 2007/7/3, Mike Kupfer <mike.kupfer <at> sun.com>:
> > > The one concern that I have about enabling font lock by default is that
> > > it can be slow, i.e., when editing large files on relatively slow
> > > hardware.
> >
> > If somebody feels it is too slow for them, they can disable it using
> > the drop-down menus or using M-x customize.  But the vast majority of
> > people would benefit from it.  
> 
> My late .02€ to the discussion: MHO is that plain vanilla font-lock is too 
> slow to be enabled by default.  [...]

I am used to GNU Emacs and new to XEmacs.  I wonder:  How slow is plain
font-lock on recent hardware (3 years old or less)?  How common is it that
people with such hardware get frustrated and decide to switch away from plain
font-lock?