I've had a love-hate relationship with playing this opening. Often very fun in blitz, I find its not so great in tournament games. My problem is shaking the bad habit of playing it!
There are two flavors of the Nimzo-Larsen attack. The first being 1.Nf3 followed by 2.b3. In this version, you usually see white playing a reversed Nimzo-Indian. I've had a lot of fun getting in funky moves like Rf1-to-f3-to-g3 and applying hard pressure on black's kingside. The downside is if your attack fizzles, black gets better chances in the middle of the board.
The other flavor (which is the one I most often play) is the 1.b3 followed by 2. Bg2. This one is a bit more double edged in that you invite black to play an e5-Nc6-d5 formation, where you attempt to attack on the flanks with e3-Bb5-f4. I've played countless blitz games where black thinks its okay to play exf4, but then I quickly play Bxg7! and then immediately play Kf1 when black counters with Qh4+. At this point white is winning so long as trade-downs are carefully negotiated.
The downside to the Nimzo-Larsen is when black decides not to play along and instead sets up stodgy formations like d6-e5-Nf6-Nc6, or c6-d5. This what I often face in tournaments, and its very hard to get an advantage if any is to be had at this point.
At any rate, I just came back from a G30 swiss tournament and went undefeated. Here was my favorite game I played from today, which I employed the Nimzo-Larsen for an easy win:
1.b3 Nf6 2.Bb2 d5 3.Nf3 e6 4.e3 a6 5.d4 c5 6.Bd3 Nc6 7.0–0 Qb6 8.Nbd2 c4 9.Be2 Bb4 10.c3 Bd6 11.Qc2 cxb3 12.axb3 e5 13.dxe5 Bxe5 14.Nxe5 Nxe5 15.c4 Qc7 16.Qc3 Neg4 17.Bxg4 Nxg4 18.Nf3 Be6 19.Qxg7 0–0–0 20.cxd5 Bf5 21.Rac1 Qxc1 22.Rxc1+ Kb8 23.Qxh8 Rxh8 24.Bxh8 Be4 25.d6 Bc6 26.Bg7 f6 27.h3 Bxf3 28.gxf3 Ne5 29.Bxf6 Nc6 30.Rxc6 bxc6 1-0
Of special note for me is how I played fundamental trade-downs once I had the winning advantage. Moves like 23. Qxh8 were not technically the best possible moves, but they ensured the safest winning advantage whilst giving black the least amount of hope for a swindle attack.