PC Stats published an interesting article on Windows Vista's memory usage. Here's an exerpt:

With 512MB of memory Vista crawls. Even in 2D office/workstation style work there was a noticeable lag. Microsoft's Windows Experience Index was particularly hard, scoring just 1.7 points. Not very impressive. What the benchmarks don't say though was how laggy simple Windows tasks were... we could hear the HDD chugging away accessing the swapfile. Increasing total system memory to 1GB was like night and day for the PC. Immediately everything was more responsive and the HDD LED was not a solid shade of orange. Not only did Vista itself register a huge bump, the Office Productivity results also got a decent boost in performance. Games also welcomed the 1GB of memory, some tests jumped 10% just by adding more system memory.

Moving to 2GB of total system memory increased the Windows Experience Index by three times, compared to what the computer scored with just 512MB of memory. In office tasks a PC is mainly user limited, so there was no major difference between 1GB and 2GB of RAM according to the office productivity benchmarks). There was a small performance boost in games when moving from 1GB to 2GB of memory as well.

If you're itching to upgrade to Microsoft Windows Vista, do yourself a favor and look at your PC carefully. Does it meet all the hardware requirements that Microsoft has laid out? If not, moving to Windows Vista may cause headaches. A few quick conclusions can be made about system memory and Windows Vista. For Vista, 512MB RAM is not enough even for word processing. It's quite a painful experience so make sure the PC has at least 1GB of memory.