from "Jehovah's Witnesses" at about.com: (http://experts.about.com/q/1617/3052543.htm)
Well, for the Watchtower doctrine to be true, that would mean that, from the first century, up until the year 1935, the number of Christians throughout history could not exceed 144,000. This is an absurdity, given a number of Biblical facts....Though the Bible never tells us exactly how many Christians existed in the first century, we do have a glimpse.
We find by reading Acts chapter 2, that 3,000 members were added on the Day of Pentecost. Then, in following chapters, we find 5,000 more converts just a week later, making over 8,000. Then, we are told at least 4 times after this in Acts, that the church continued to multiply and increase rapidly. Yet, the JWs expect us to believe that, from the first century to the year 1935, only 144,000 Christians had ever existed? I find that absurd. Let's do the math....
The only concrete numbers that Acts give us are the 3,000 on the Day of Pentecost, and 5,000 more a week later, making 8,120 (there were 120 in the upper room). That would mean that, after that first week, for the next 1900 years, the church averaged gaining only about 72 converts a year! Yet, this is the exact opposite of what we read in Acts, where we are told at least 4 more times that the church continued to grow! (Acts 2:41, 4:4, 5:14, 6:7, 9:31, and 11:24).
Google added the highlighting, based on my search terms.
So 8,000 were added to the 120 in the first month. Looks like a pretty pitiful snowball if it can't accumulate another 136,000 in the next few decades. (Recall that the "apostasy" would have rendered 1900 years of nominal christians inelligible for anointing, save for folks like Charles 'It's all in the Pyramids' Russell...)