I've been using small, lightweight wallets for years so I could keep them in my front pockets.  I was never a money clip kind of person.  I warmed to the Slim Clip quickly, though: it's very thin, durable, lightweight, and it holds your cash and cards snugly.  I've been using it for about 2 months and am very happy.  As a long-time wallet user, the biggest adjustment for me after moving to the Slim Clip was having to always fold bills neatly together before sliding them under the clip (it's a lot more exacting than a wallet).  It's not a big deal, though (and it has the added benefit of keeping your cash well-organized).

Someone in another review complained that the clip for the credit cards broke off when it was dropped.  That is impossible: the Slim Clip is formed from a single piece of folded stainless steel.  You'd need a band saw to break off the clip part.

Update: July 2016.  I still use this wallet all the time.  7 years later it's still holding up like a champ.