Have 2 desktops and two laptops all with SSDs installed. For me there is no going back to a HDD for OS + Programs. That said, as geofelt stated it is a personal choice - money vs performance gains:
What an SSD speeds up:
.. OS load time, typically around 15 Sec (depends on number of start up programs).
.. When runing a program it will load in one, or two blinks of the I. I can click on a recent link, excell spreed sheet and it will load excel and the spreadshet before I could even move the mouse to a cell (NOTE: my spreed sheet is also on the SSD.
.. Any operation that involves loading a file from the Drive is much faster, providing that file is on the SSD.
SSD will NOT:
.. Will not sped up post time, Just the time from start loading operating system to that spining ball goes away.
.. Speed up a program that has been loaded, that is Word, excell do NOT run faster.
.. No Increase in FPS for Games, ingame maps that are call, will load faster PROVIDING the map is on the SSD.
.. email, surfing the web, and downloading files from the Web are NOT speeded up, as down load speeds are much slower than even a HDD.
.. Geofelt mentioned windows Updates, Downloading the update is not improved, only the install of the file after it has been downloaded - and that is if you have not redirected downloads to the HDD as many have.
My Wife HATES long boot times, even if it is only once a day, or once a week (she leaves her system on just so she can avoid that wait). As soon as I can "fix" here system, I already have one of two SSDs to go in there.
So - Boils down to how often you boot your computer, if only once a day, or once a week and it only takes a one, to one and a half minutes to boot into windows, Then how satisfied are you with program loads: These are questions only you can answer.
@ jsrudd - 10->15% is more a Minimium recommed, personally I prefer (as geofelt) the 20 to 25% free.