This is one of the many Techno-phobic movies that sprouted like mushrooms in the mid-90s, after the Internet went mainstream.
Hollywood movies have always had their way in "beautifying" the depicted ongoings, to make them look better and more appealing. The same happens when Hollywood tries to show us some hi-tech. The outcome of such attempts varies from being very far-fetched and ridiculous (see Hackers (1995), Johnny Mnemonic (1995), etc.) to being quite realistic (see Sneakers (1992)).
"The Net" lies somewhere between those extremes. By nitpicking, one can end up with quite a lot of technical inconsistencies, and a lot of cases where the ongoings seem to be much more "sexy" and graphical than the way things are in real life (as usually happens in movies).
However, by simply overlooking those, the viewer ends up with a quite solid, entertaining movie. The characters and acting are convincing, and the movie does a good job in keeping you in your seat till the end of it. The plot is okay (a fairly standard one, really -- based on the good ol' paranoiac design, but with a hi-tech edge this time), and quite convincing (again, when disregarding technical issues). The development of the plot is a bit sluggish, though, and occasionally you can anticipate some supposedly surprising turns in the plot.
The bonus here is cutie-pie Sandra Bullock, which besides being cute (something she does quite easily, apparently), also portrays a solid act. You can really feel her character -- her despair, her emotions.
In the bottom line, the movie is entertaining and interesting, rates about 7 from 10 in my scale. It's worth renting from the video library, or even watching in the cinema. Whether to buy it or not is up to you.