In this week's Barron's [a paid service], there's an in-depth look at the mega IPO of the Blackstone Group (NYSE: BX). It's the most important IPO since the offering of Google (NASDAQ: GOOG), although investors shouldn't expect the same kind of returns.

While Google signaled a burst of growth in online advertising (which appears to be long-term), it looks like Blackstone is really signaling a top in the private equity space. Why?

Here are some bullet points:

Competition: KKR, Goldman Sachs (NYSE: GS), TPG, Apollo Management and others all have big war chests and are competing for deals. This drives up valuations -- making it more difficult to get strong returns. This is essentially what happened with venture capital during the internet boom.

Institutional Pushback: Institutions and hedge funds are pushing for higher prices on buyouts. An example is the Clear Channel (NYSE: CCU) deal.

Higher Interest Rates: Private equity has been blessed with dirt-cheap interest rates and this makes it easier to generate returns. But with interest rates climbing, things are getting more difficult.

Politics: Capitol Hill needs more tax revenues. So why not raise rates on private equity?

Yes, Blackstone has posted a stunning 22.6% average annual rate of return (adjusted for fees) since 1987. But, with all these ominous trends, will Blackstone continue the pace? And, is it worth paying 2 times the multiples of companies like Goldman Sachs and Morgan Stanley (NYSE: MS)?

Tom Taulli is the author of various books, including the Complete M&A Handbook and the EDGAR-Online Guide to Decoding Financial Statements.