If you have the ability to download on your system's computer, I suggest that you try Mozilla's new Firefox browser. I have been using it exclusively for the last few months (starting with the beta version), and I have noticed that the problems of pop-ups and annoying ads don't occur. I'm told by my son-in-law (who is our home network guru) that the security puts Microsoft products to shame.
I also love the ability to create tabs in a single window. They're easier to close when I want to return to the previously open tab than the multiple windows in IE or Netscape.
I've experienced no difficulty with viewing any sites. It doesn't appear that incompatibilities are much of a problem. Either that, or website developers are getting savvier about not using browser-specific tags.
There's also a new email viewer, called Thunderbird, that many are calling an "Outlook killer". I haven't tried it - I generally use my Yahoo account, or Popmail.
In general, the Open Source software that I've tried is functional and easy to use (Open Office, Linux, Firefox, etc.). I must caution, however, I don't generally push the envelope. I'm a lazy user - if the software does 80-90% of what the commercial product does, I'm satisfied with it. Minor differences don't bother me.