Groupon is supposed to be one of the 24/7 Wall Street Top 17 IPOs to Watch in 2011. That hasn't changed, but our skepticism is growing at the same time that internet valuations for these emerging social web companies is ballooning. Our biggest concern regarding Groupon is that there are literally no barriers to entry. We wanted to feature just some of the large companies which matter, along with some of the smaller public companies which may be able to give Groupon a run for the money.