I experienced SS once from a combination of Tramadol and Effexor; however, I was on a fair whack of Tramadol at the time (above the maximum recommended amount by a couple hundred milligrams) so probably not a huge surprise that if you drop an SSRI or SNRI in on top of that there's going to be an increased risk. Not that my GP at the time seemed to take any of that into account when they started sending out alert notices about Tramadol and other med combinations. Obviously I wasn't taking Effexor again after landing in hospital, but despite my not taking any other serotonergic medications on top of the Tramadol, he panicked and pushed me to come off the Tramadol by itself also.
And of course stupid me decided to listen to him, weaned off the Tramadol, spent several months then basically being almost completely non functional (I eventually changed GPs and made an informed decision to recommence the medication). There was absolutely no reason for me to come off of Tramadol in the first place, I'd already lowered my dosage from around 600 mgs to 400 (which is what I'm on now), the medication was doing what it was supposed to be doing with little to no side effects, and I wasn't on any other serotonergic meds at the time. As far as I'm concerned the decision back then to pull me off Tramadol in the first place was not even remotely based on any sort of best practice risk management.
Since then I've been on Deptran and Mirtazipine (not at the same time), on top of taking Tramadol, and I haven't had any problems whatsoever (apart from perhaps being a bit knocked out until my body adjusted, and experiencing some weight gain, which for me isn't actually a bad thing). I trust my Psychiatrist to know about risk management when it comes to prescribing medication to individual patients, not just have a Doctor who hits the panic button because he receives an alert telling him that there may be a risk of SS with certain medications.
And yes, Serotonin Syndrome can be a frightening and horrible experience, but from what I was told when they were preparing to release me from Emergency it's also quite rare. So why start chopping and changing patient medications based on a very small risk factor, especially when the benefits of certain medications are clearly outweighing any minor risk.