The first ever TrainSignal course that I “took” was David Davis' VMware vSphere 4 training. I had heard lots about it from a few people on Twitter and several others in person and I wanted to use it to fill in a few gaps in readiness for my VCP4 exam. I've since been through a few other courses and they've all been great.
What's changed between then and now is TrainSignal's transition from supplying only DVDs, through adding online access to purchased course, to finally switching to a subscription only model.
It's a move that makes a great deal of sense and it'd be worth a subscription to get access to course related to technologies that I don't use as often. There is even an offline player but it's currently limited to desktop computers (Windows / OSX).
One thing that I would like to see though is a way to view courses offline on mobile devices. I recently used Handbrake to transfer my copy of Scott Lowe's Designing VMware Infrastructure to my iPad so I could work through it anywhere. At about 800Mb though, I would only want to download that ahead of time and not via 3G when on a train.
Still, good move TrainSignal. I like it.