Getting over a hundred errors is good. It means you made one mistake near the beginning; once you fix it, all the others will disappear. Getting a dozen or two errors is bad. It means you made a dozen or two separate mistakes :)
My personal record is 45,000 bona fide errors. But that wasn't from a w3c validator; it was from a specialized tool that also looked at things like incorrect punctuation and capitalization, unfamiliar letters and mismatched brackets. In a 500-page work produced by the Early English Text Society, this kind of error can mount up very very fast. Fortunately you can also ignore the report very very fast ;)
Beware of Tidy. I have never found a version that simply reports errors without "fixing" them, no matter how emphatically I tell it not to change anything.
You can also get interesting results in "validate by upload" if your finger slips and you feed in a plain-text file instead of HTML.