This is turning out to be a very interesting thread.

I tend to agree with Markd's comments, but a lot of other valid points have been raised.
In my personal view on having a MSc(CS), the biggest difference is this: Having one will probably make a difference in your salary, even if only slightly, by virtue of higher qualifications entitling you to a higher salary... but that's not always the case. That's it.
An MSc does not make you a better developer, but a better computer scientist. No they're not the same, but that's a whole other discussion. It comes down to practical vs. academic. This translates into the same distinction between work experience and qualifications. Therefore it would make sense to have one if you want to specialise in a specific field (as mentioned previously in the discussion). On the other hand, not having a MSc does not automatically exclude you from applying for a job that "requires" one (job ads generally describe their /ideal/ candidate). It would be shortsighted of a company to consider only MSc graduates and I, personally, would probably not want to work for such a company anyway. Most of them don't, though.
As Gnome mentioned there are absolutely brilliant people who have no or only "basic" CS qualifications and that is certainly also the case in my experience. Conversely I know MSc graduates who wouldn't be able to code their way out of a simple if-statement.

Of all the top devs I know, only 2 of them (IIRC) have MSc degrees and it's not the degree that earned them that reputation.
I, for one, will not be doing my MSc... unless it's "free" (ie. I get paid my current salary for studying full-time)... and I get to research something that I'm *really* interested in... so probably not.
Oh, but hons. is a whole different story. It's worth getting one of those.
