I like Wikipedia; so much infact, that when searching for information in Google, I've got into the habit of prefixing 'wiki' in front of whatever term I'm looking for, because I'm pretty sure wikipedia will have an enlightening/well-written/interpretable entry; perhaps a basic entry, but that's sometimes the best place to start.
Anyway; just today I've noticed, perhaps I didn't need to type 'wiki mushroom' to be assured of a wikipedia page about mushrooms being high up in the ranking. Based on a random check, of what I deemed to be 32 completely unrelated terms across a number of 'fields of interest' 88% of those had a wikipedia entry on the first page, of those, 70% had the wikipedia link as the first entry. Here's my raw data:
These had a wiki page as the first link
These had a wiki page as the second link
These had a wiki page somewhere relatively high on the first page
overture (knocked down because it seems to be a yahoo trademark)
These didn't seem to have a link on the first page
google (worth a try =P)
I think anyone would agree those are all quite unrelated, except maybe by association as I was typing (while sitting on a chair by a window, half watching television, smoking a cigarette and wishing I had a coffee; clearly).
I wonder, if Google's liking Wikipedia based on a wealth of ALL content, or a high relation to a single query.. Considering that the first links, in all cases other than those where a wiki link was first, were singular across the set of queries (i.e. there is no quantifiable 'second place' for a single domain meeting those queries); that's some pretty good going for Wikipedia, if you're interested in researching cabbages and quaternions.