I wouldn't go so far as to say that VPN's are useless, but they certainly are much less beneficial than a naive user would think (most such users think adding more hops always means more anonymity, hence the 'good luck I am behind 7 proxies meme'). If you are monitored by your ISP, using a VPN can hide that you are using Tor, but your ISP is still able to do one half of a timing attack against you. The biggest advantage of using a VPN is that it hides that you use Tor from your ISP. It also gives you a static entry node in most cases, so if you happen to form a compromised Tor circuit the Tor internal attacker is only capable of tracing you back to your last VPN node. Of course if your VPN entry node is malicious the attacker can still do a timing attack against you (and your ISP always can). Using a VPN prior to Tor is not really insecure per-se, the primary effect it has is changing it from trusting your Tor entry guard the most to trusting your VPN provider the most. I think that this can be beneficial, I don't think many people trying to attack Tor would run VPN services taking into consideration that some Tor users might enter through a VPN first, but I don't put it past the feds to be running several commercial VPN providers (and they definitely have operated VPN's in the past for criminal stings, but usually advertised on criminal forums, which is why you *NEVER* use a VPN that you first heard about on a criminal forum). On the other hand, if your entry node of Tor is bad, and your Tor circuit falls to a timing attack, the VPN is the only thing keeping you safe, which is better than nothing but historically most VPN's are broken by the feds after enough time in court. VPN's tend to buy time at best, tho I have heard of a few cases where the feds failed to trace targets through VPN's, in the majority of the cases the VPN only slows them down though and after enough months they will be able to trace you, and most people keep using the same VPN indefinitely so.