It's a relatively small business ($2 bln, in IBM's $90 bln annual revenues...) and it's not profitable because of the massive competition. Besides, IBM is shifting focus from hardware to services/solutions, and so far (as its financial reports/forecasts) show, they are on the right track.
Additionally, it appears that with this deal, IBM will own 20% of Lenovo and Lenovo will use IBM's computing/financial services. Now this is smart ! A big step into the biggest emerging market in the world, owning 1/5th of China's largest computing company.
I wonder what will IBM do with the extra cash. They usually buy some other business (last time it was Rational and PwC Consulting, with money from the sale of the HD business to Hitachi).