This could be bad. I'm not terribly concerned if Comcast discovers my secret passion for muscle cars and I get more ads for car customizing kits. It might be annoying, but I'm not doing anything I really want to hide. Where the problem could occur is if ISPs start inserting their own ads in place of ads by, say, ZDNet. That could cut off the revenue that keeps websites alive, and that could have very serious repercussions.
Authentication that occurs during the creation of a PPTP-based VPN connection uses the same authentication mechanisms as PPP connections, such as Extensible Authentication Protocol (EAP), Microsoft Challenge-Handshake Authentication Protocol (MS-CHAP), Microsoft Challenge-Handshake Authentication Protocol version 2 (MS-CHAP v2), CHAP, Shiva Password Authentication Protocol (SPAP), and Password Authentication Protocol (PAP). PPTP inherits encryption, compression, or both of PPP payloads from PPP. For PPTP connections, EAP-Transport Layer Security (EAP-TLS), MS-CHAP, or MS-CHAP v2 must be used for the PPP payloads to be encrypted using Microsoft Point-to-Point Encryption (MPPE).
The downloader. Whether they’re downloading legally or illegally, this person doesn’t want on some company’s witch-hunt list just because they have a torrenting app installed on their computer. VPNs are the only way to stay safe when using something like BitTorrent—everything else is just a false sense of security. Better safe than trying to defend yourself in court or paying a massive fine for something you may or may not have even done, right?
Cost - VPNs aren't too pricey, but they vary from vendor to vendor. If your main concern is price, then go with something inexpensive, or free - like Spotflux Premium VPN or AnchorFree HotSpot Shield Elite. By all means, try a free server but they do have a few drawbacks since they attract a lot of users. Free servers are often slower, and since most are ad-supported, they place adverts on the online pages you access. Others can even limit the speed of your connection, as well as your online time or amount of data transferred.
Think about it this way: If your car pulls out of your driveway, someone can follow you and see where you are going, how long you are at your destination, and when you are coming back. They might even be able to peek inside your car and learn more about you. With a VPN service, you are essentially driving into a closed parking garage, switching to a different car, and driving out, so that no one who was originally following you knows where you went.