Yes, I would unequivocally say Wikipedia is a good resource. I'd go even further than that and say it is an excellent resource - but then, I have been an editor there for 18 months now...
The thing with Wikipedia is that it has got a bad reputation for reliability due to its early life. It is only within the last year or so that sourcing has been held as one of the most important things on the site, and rightly so. In some articles, for example any of the Featured Articles, you will see a level of detail and quality that the majority of traditional encyclopedias lack - yet they are not acceptable as a source due to a lack of understanding of how the site works and how to use a permalink.
Yes there are plenty of stupid pranks that occur but the majority of them are fixed within seconds.
I think, even if it is not used as a direct source for people's schoolwork it is an excellent starting point to send people off on a research trail - just follow the cited sources...