For what we generally use Blender for i.e. content developed for games, the core application is stable enough. I'm not producing much actual content these days but writing up the tutorials means I'm doing a few things in more depth and have yet to have any application issues. Having said that, 2.5 obviously doesn't have the 'maturity' of 2.49 as a production tool (import/export scripts etc), and whilst the user-base grows, the demands that requires in terms of tools and scripts just can't keep up. I personally think Blender has got to the point where they need to hire a full time team instead of having people work on something for a while to get their skill 'l33tified' only to have them transfer to something more lucrative.