When I'm using my primary computer, I'm usually just go away when I'm done, so anything that is save in the virtual memory fetch is there when I return. I'm assuming here, of course, but I don't think that it clears out the cache unless there is a memory pressure. I can certainly see an increase in the amount of memory that my session is taking whenever I run for long periods of times.
My current uptime is 23 days (reboots are purely windows update ones), and applications luanch are nearly instantenious. This is not the same on my laptop. I can't keep it always on, so every time I start working with it, I need to bring things to memory, which may take some time. Imagine waiting for VS.Net to load from a laptop (usually slow) HD. Yuck.
Cold boot - VS.Net start on my main computer:
3 seconds to start screen, 14 seconds to start page being usable.
Opening VS.Net after it has been opened:
Instantenous start screen, 4 seconds to usable start page.
The cold boot times are probably double that on a laptop, so imagine how good it is to get the good times on the first time.