I am using a 47uF 10V SMD capacitor (GRM31CR61A476KE15L) mainly for DC blocking. But it make a phase shift on the signal, we can deal with this phase as long as it remain constant(hence the capacitance is constant too). 
After 60 days the performance of the circuit has degraded, the capacitance has been reduced to 35uF. By accident I have soldered it again and the capacitance return to 44uF (which is in the tolerance range +/- 10%). I read about this and found this page, talking about aging in high dielectric constant capacitors and the curing occur by temperature when soldering.
I really got shocked by this fact. So the question is how expert designer, design devices that could work for 10-15 years without degrade in performance with such phenomena?
Answer
You must pick your capacitor technology bearing in mind your intended use.
X5R (Or worse Y5V) is not really the smart choice for filters (Which is what you have if you care about phase shift thru the cap), apart from anything else you will have built a voltage controlled phase shift network as applied DC across that cap will cause SIGNIFICANT changes in value (This gets much worse with smaller case sizes).
C0G is generally ok for this sort of thing, but you will struggle with finding more then about 100nF or so. The other option is film or maybe a bipolar electrolytic (If going here make the value LARGE, so the phase shift is negligible over any reasonable amount of drift).
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