Over the last few years, a growing number of studies have explored how Aspect-Oriented Programming (AOP) might impact software maintainability. Most of the studies use coupling metrics to assess the impact of AOP mechanisms on maintainability attributes such as design stability. Unfortunately, the use of such metrics is fraught with dangers, which have so far not been thoroughly investigated. To clarify this problem, this paper presents a systematic review of recent AOP maintainability studies. We look at attributes most frequently used as indicators of maintainability in current aspect-oriented (AO) programs; we investigate whether coupling metrics are an effective surrogate to measure theses attributes; we study the extent to which AOP abstractions and mechanisms are covered by used coupling metrics; and we analyse whether AO coupling metrics meet popular theoretical validation criteria. Our review consolidates data from recent research results, highlights circumstances when the applied coupling measures are suitable to AO programs and draws attention to deficiencies where coupling metrics need to be improved.