It is quite common for a bull market to last far longer than many would have thought, and even more so after the brutal economic downturn we had in 2008-2009. Only just recently did U.S. stocks surpass the previous market top reached in 2007. Although it does not mean that a correction is definitely imminent, the current stock market rally is the longest the U.S. has ever seen without a 5% correction. Ever. Dig deeper and we can begin to see some froth in many high-flying market darlings. Fortunately, we are not anywhere near the bubble conditions of the late 1990's, when companies would see their share prices double within days just by announcing that they were launching an e-commerce web site. However, some of these charts have really taken off in recent weeks and I think it is worth mentioning, as U.S. stocks are getting quite overbought. Here are some examples:

TESLA MOTORS - TSLA - $30 to $90 in 4 months:

NETFLIX - NFLX - $50 to $250 in 8 months:

GOOGLE - GOOG - $550 to $920 in 10 months:

You can even find some overly bullish trading activity in slow-growing, boring companies that do not have "new economy" secular trends at their backs, or those that were left for dead not too long ago:

BEST BUY - BBY - $12 to $27 in 4 months:

CLOROX - CLX - $67 to $90 in 1 year:

WALGREEN - WAG - $32 to $50 in 6 months:

Ladies and gentlemen, we have bull market lift-off. My advice would be to pay extra-close attention to valuation in stocks you are buying and/or holding at this point in the cycle. While the P/E ratio for the broad market (16x) is not excessive (it peaked at 18x at the top of the housing/credit bubble in 2007), we are only 15-20% away from those kinds of levels. Food for thought. I remain unalarmed, but definitely cautious to some degree nonetheless, and a few more months of continued market action like this may change my mind.

Full Disclosure: No positions in any of the stocks shown in the charts above, but positions may change at any time