It's a pity Kittenstomp seems to have taken a break... he's playing just such a character in my Loralton campaign (Amorph, who's currently locked in APS: Putty form).
Anyway, the obvious answer is that those powers with disadvantages/drawbacks/penalties/etc. when the power is active would pretty much be in effect 24-7-365. For instance, someone with permanent APS: Metal would always be at 4x his/her 'normal' weight (or what he/she would weigh in normal, human form) and only 1/2 of his/her 'normal' speed. In addition, this APS: Metal form carries an optional Horror Factor of 13, which means that he/she is going to freak people out wherever he/she goes.
But beyond the disadvantages listed in the books, there are some significant mundane ones as well. Again, let's take Metal-Skinned Bob with permanent APS: Metal as our example.
1. Bob will find it difficult to fly commercially while locked in his metal form, as it sets off every metal detector in the airport. At best its a serious inconvenience as he's tested/searched again and again.
2. Since metal holds heat well, if Bob's out in the sun too long he better douse himself with water before touching anyone... otherwise they could easily be burned.
3. If Bob's metal form is iron or an iron alloy (such as steel) certain magnetic forces could easily be an inconvenience or even painful.
4. Four words -- RUST IN EMBARRASSING PLACES.
5. Any attempt to administer medication to Bob via injection would fail in metal form ("Bob, you bent the syringe needle AGAIN!"). This could be downright serious if Bob ever becomes a diabetic. The same is true if he ever requires surgery.
6. Bob would need to be extra careful with his Superhuman-level strength, or else be the cause of lots of accidental damage/destruction ("I'm sorry, I didn't know that crate of anvils was so heavy -- otherwise I would have NEVER stacked it on top of that crate of rare Wedgewood china!").
7. Any situation that involves factoring in the weight capacity of operators/passengers will be problematic for Bob -- including crowded elevators, riding bicycles/motorcycles, certain types of furniture, etc.