Good managers take advantage of that unquantifiable feeling. Great manages inspire it...

:w00t:

And geek personalities tend to thrive on it.

I never felt bad about inspiring "silly" hours out of my developers and testers, because I was there with them for every hour of it -- and because we compensated them well for it: buying back missed vacation time, bonuses for delivery and lots of slack time after we delivered. Our salaries went the opposite direction of the dot-bomb curve because we put our backs into the work, figuratively speaking.

Did it help our careers? Absolutely. Not at that start-up company, of course, but everybody who played on that team has taken the skills that we honed there and moved on to much more lucrative, much less stressful career options that they couldn't've gotten without the trials-by-fire.

In the US, my experience is that if you want a better job or a raise, you usually have to change companies (unless the company is large enough to support internal transfers), so you have to make sure that the "silly" time that you invest in a project is something that you can use to improve your resume when it comes time to move on.