There are other reasons investors are becoming a bit more cautious. While home prices rose in August from a year earlier at the fastest pace since February 2006, the gains slowed in September—suggesting that prices are peaking.
"Our view remains that national home prices will continue to rise," says Peter Newland of Barclays. "That said, this report may hint at the beginning of an easing in the pace of price gains."
As for third-quarter corporate earnings, they've been respectable—but nothing to write home about. Profit growth remains slow and steady. Third-quarter profit growth among S&P 500 stocks is expected to be about 4.5%, and companies are beating a low bar set by analysts, investors say.
Still, some analysts say the overall market is reasonably priced, no matter how expensive a few sexy stocks appear.
The S&P 500 trades at a reasonable multiple of 15 times expected earnings over the next 12 months. Unlike 2000, the stock market doesn't seem in a precarious position, based on price/earnings ratios and other metrics.
There's "a little frothy speculation around the edges, but overall technicals still remain reasonably healthy," says Mr. Ablin.
"One big difference this time is that nearly 100 stocks of the S&P 500 are making new highs along with the index," he says, suggesting that many stocks are joining in the climb, a healthy sign for the overall market.
Tobias Levkovich, Citigroup's chief U.S. equity strategist, argues that there's a healthier mind-set among investors today than in 2000. He says he's cautious but isn't telling investors to dump stocks.
"I'm concerned that earnings guidance has been relatively soft—there's a real divergence between what the market is doing" and what companies are reporting, Mr. Levkovich says. "And I do see a certain level of complacency, but it's not exuberant."