It really depends on the spyware as to how much info they see...
What is commonly called "spyware" is really a less dangerous form of Trojan horse... They range from just annoying, to potentially revealing a bit too much of yourself...
The worst spyware programs are Xupiter and Bonzi Buddy... They do all sorts of things, including change your settings (such as changing your home page and search page) load up ads (that you can't always block, and even if you can the sheer number they load will grind your system to a hault) and track your internet usage... They DO really track you, many of them, and besides that, are often responsible for crashing systems... They cause a lot of instability...
The sad thing is some of them (such as C-Dilla) are given with legitamate well known software... (c-dilla monitors your optical drive's usage to catch people pirating the software that uses it...) but most (like bonzi) come with less important bits of shareware as a means of those people getting money even though they're not selling their product... They are often VERY hard to uninstall, and some of them have very virus-like qualities...
To block pop-ups, I do two things:
Since sometimes pop-ups are legitamate, it has to be smart, so there is one pop-up blocker that you have to "train" called analog-x POW which I quite enjoy... Some crafty annoyers get around that by adding random numbers and letters to keep you from blocking (requiring you use wildcards, not too hard to learn) or worse, short circuiting the thing using wildcards in the beginning of the window name "***Attention: Free Spam here***"
In addition to that, I also put certain really nasty (by that I don't mean pornographic, but that applies too) sites in my "restricted" section in Internet Explorer... Ever since I did that, my problem with ambush websites has dramatically decreased... I put tripod in there, and a few "search/gambling/trip to batswana" sites... You know, the ones that register themselves as things like "www.rpgsarecool.com" or "toendallwars.com" (the latter made me mad... Argyll films lost their domain name, and an ambush site took over in a very short time...)
Those things suck... So, those two methods are good... For restricted sites, tell them NO ACTIVE X, and no metarefresh and no accessing secondary sites... Basically, no to everything (unless no means more permission, then tell that yes) and it really helps out...
For real trojan horses (and also for viruses) I use
http://housecall.trendmicro.com/housecall/start_corp.asp which is free and it cleans them too! It's really nice, and doesn't become a drain on resources like a resident virus scan does.