Bart Ehrman likes to tell his readers and listeners that there are hundreds of thousands of textual variants in the New Testament manuscript tradition, knowing that readers and listeners who are unfamiliar with what qualifies as a textual variant will be misled by this number. In reality, the vast majority of textual variants are simple spelling differences (e.g., spelling the Greek name for "John" with one "n" or two), and almost all other variants either do not affect meaning at all (e.g., synonyms) or they arise late in the manuscript tradition and therefore have nothing to do with the original text. Less than one percent of textual variants are both meaningful (i.e., they would affect our translation of the text) and viable (i.e., they may go back to the original text). Of the variants that are both meaningful and viable (the only variants that are really important), not one of them changes any significant Christian doctrine. The result of New Testament textual criticism, then, is that Christian doctrine and the texts it is grounded in are firmly established—hardly the message one would get by reading Ehrman!
Here's a brief discussion of variants by Daniel Wallace, one of the most respected New Testament textual critics and Greek scholars of our time.