Since someone mentioned ProductCenter from Softtech, so I have to take this jab.
Even if you do have a successful third party implementation, PTC can dump them from their certified third party program at any time. At least that's what PTC has done to Softtech. Softtech is no longer allowed to update their software to work with PTC's software. There are some convoluted ways around this issue which all seem pretty silly to me (read: "pay money to PTC).
You might argue that Softtech did something wrong to PTC to force this issue. But PTC would never give an explanation (I asked over and over again). And if Softtech did do something wrong and deserved to be booted, it still shouldn't be a revenue increasing opportunity for PTC (they recommended the software!). PTC's solution (if you didn't want to switch to a PTC PDM solution) was to have every customer purchase a $20,000 (+yearly maintenance) of Toolkit. Sounds like a win-win situation to me.
What SofTech did wrong was to position themselves so that they required the use of Toolkit to enable their PLM solution to function with Pro/E.
I'm very surprised that SofTech was allowed to use Toolkit this long to enable their PLM solution. After all, PTC has been a PLM software company since 1998 - it doesn't make any business sense for them to allow a 3rd party to use PTC products to create a piece of software that competes with their own products.