I took my non PTFE tubes out and replaced them with PTFE ones after I used the printer for about 2 months. The biggest problem was that when you switched on the filament would not feed no matter what you did. It had either unloaded itself as it cooled down or it was blocked solid.

I think these problems only apply to ABS though, not PLA, PLA does seem to be a lot better behaved though I do prefer the parts ABS makes, they are a lot more forgiving in use and a lot easier to machine after they are made.