No system wide club agreements as far as I know, but TW has clubs at both ORD (Northwest) and BOS.

As far as flying TW, I'm happy w/ my Elite 1 status. Upgrades are generally extremely easy, except for the popular morning flights to/from STL and East Coast business centers. Service is usually good to very good, with catering lacking some. A lot more personal feeling service than most airlines, without some of the polish at times. However, I'd take F on TW over Y on UA anytime. And the 757s and 767s are quite nice up front. And while STL can get bad when the weather hits, TW's operational numbers have been quite good.