I've been a member. It's a great value if you travel by yourself to airports with clubs that wouldn't be covered by your main carrier's program.

Remember AmEx Platinum benefits as well.

The disadvantage is that you have to pay for any guest on any program, unlike most airline programs.

I would even say that if you're doing critical and/or time-sensitive travel (where flight cancellations/delays will cost you significant $) even just a few times a year to those airports that you wouldn't be served by under your carrier's program, it may be worth it as an 'insurance policy' as agents in those clubs that you otherwise wouldn't have access to may mean the difference between having your plans work out and not.