Frames on web sites

We are looking at changing our web site to include a top naviagtion frame. I read a lot about how bad frames are but then I downloaded and looked at many of our competitors front pages using an HTML program and most use them too.

Are there really issues concerning the use of frames on web pages? Will a frame limit my customer’s abilities to look at my site or navigate it and how?

2 years ago we believed that most PCs were running earlier versions of IE and Netscape. Does anyone know of a compenhensive web site that has evidence of what browser software more of the population generally use now?

Much obliged.
Bruce