A trader in the Nasdaq 100 stock index futures pit at the Chicago Mercantile Exchange watches prices for electronic dealings in the contract November 22, 2000.ReutersBill Smead warns of a market bubble similar to the dot-com era in 2000.Investor exuberance around AI has driven much of the S&P 500's 157% rally since March 2020.High equity ownership and a penchant for risk-taking signal a bubble, Smead says.Bill Smead has only seen this once before during his 44-year career.Investor exuberance about revolutionary technology, extremely lofty expectations, a penchant for risk-taking on highly volatile assets: For this generation of investors, this particularly strong cocktail of animal spirits that has driven the S&P 500's 157% rally since March 2020 can only be compared to the dot-com bubble era leading up to 2000, Smead said in a December 10 note.Smead is a highly successful long-term value investor, with his Smead Value Fund (SMVLX) beating 98% of similar funds over the last 15-year period, according to Morningstar data.