Monitor calibration program vs. Adobe gamma

I'll be expecting a new monitor shortly - either the NEC 20WMGX2 or a Dell 2007WFP. I am wondering how essential it will be for me to buy monitor calibration software. I use Adobe CS2 and have access to Adobe Gamma.

I don't print my photos - I prefer to view them on the big screen. I share them by posting them to the web. I realise programs like Spyder are essential for those who want prints to match the color representation they have achieved onscreen. But will not Adobe Gamma be sufficient for someone like me who views their digital shots online?