Primusrun works better than optirun. You may want to try running the game with primusrun.

When I open the primusrun the steam does not recognize the graphics card from Nvidia.
But other things works fine, as in glxspheres:

elijunior@dell-ubuntu:~$ glxspheres
Polygons in scene: 62464
Visual ID of window: 0xa0
Context is Direct
OpenGL Renderer: Mesa DRI Intel(R) Sandybridge Mobile
59.751339 frames/sec - 66.257370 Mpixels/sec
59.791479 frames/sec - 58.586561 Mpixels/sec
59.782424 frames/sec - 58.577689 Mpixels/sec
59.766885 frames/sec - 58.562462 Mpixels/sec
59.776034 frames/sec - 58.571428 Mpixels/sec
elijunior@dell-ubuntu:~$ optirun glxspheres
Polygons in scene: 62464
Visual ID of window: 0x21
Context is Direct
OpenGL Renderer: GeForce GT 540M/PCIe/SSE2
112.108144 frames/sec - 125.112689 Mpixels/sec
121.245602 frames/sec - 124.694073 Mpixels/sec
124.587175 frames/sec - 122.076494 Mpixels/sec
121.570910 frames/sec - 119.121013 Mpixels/sec
elijunior@dell-ubuntu:~$ vblank_mode=0 primusrun glxspheres
Polygons in scene: 62464
ATTENTION: default value of option vblank_mode overridden by environment.
ATTENTION: default value of option vblank_mode overridden by environment.
Visual ID of window: 0xa0
ATTENTION: default value of option vblank_mode overridden by environment.
ATTENTION: default value of option vblank_mode overridden by environment.
Context is Direct
OpenGL Renderer: GeForce GT 540M/PCIe/SSE2
primus: sorry, not implemented: glXUseXFont
250.729771 frames/sec - 269.391592 Mpixels/sec
282.912920 frames/sec - 277.211659 Mpixels/sec
281.262480 frames/sec - 275.594478 Mpixels/sec
282.411324 frames/sec - 276.720171 Mpixels/sec
279.904203 frames/sec - 274.263573 Mpixels/sec

More with ~$ vblank_mode=0 primusrun steam

Informações do processador:
Fabricante: GenuineIntel
Velocidade: 2201 Mhz
8 processadores lógicos
4 processadores físicos
HyperThreading: Suportado
FCMOV: Suportado
SSE2: Suportado
SSE3: Suportado
SSSE3: Suportado
SSE4a: Não suportado
SSE41: Suportado
SSE42: Suportado

Informações da rede:
Velocidade da rede:

Versão do sistema operacional:
Ubuntu 12.04.2 LTS (64-bit)
Nome do kernel: Linux
Versão do kernel: 3.2.0-37-generic
Consórcio do Servidor X: The X.Org Foundation
Versão do Servidor X: 11103000

Placa de vídeo:
Driver: Intel Open Source Technology Center Mesa DRI Intel(R) Sandybridge Mobile

Versão do driver: 1.4 (3.0 Mesa 9.0)
Profundidade de cor da área de trabalho: 24 bits por pixel
Taxa de atualização do monitor: 60 Hz
VendorID: 0x10de
DeviceID: 0xdf4
Número de monitores: 1
Número de placas de vídeo lógicas: 2
Resolução do monitor primário: 1366 x 768
Resolução da área de trabalho: 1366 x 768
Tamanho do monitor primário: 13,54" x 7,60" (15,51" diag)
       34,4cm x 19,3cm (39,4cm diag)
VRAM primária não detectada

Placa de som:
Dispositivo de áudio: Intel CougarPoint HDMI

Memória:
RAM: 7880 Mb

Outros:
Idioma da interface: Português (Brasil)
LANG: pt_BR.UTF-8
Microfone: Not set
Total de espaço disponível em disco: 75235 Mb
Maior bloco livre do disco rígido: 60896 Mb

Software instalado:

Relatórios de falha recentes:
Wed Feb 13 18:10:32 2013 GMT: file ''/tmp/dumps/assert_20130213161029_1.dmp'', upload yes: ''CrashID=bp-5c501c08-75e9-437b-a8c0-382222130213''
Wed Feb 13 20:07:05 2013 GMT: file ''/tmp/dumps/assert_20130213180700_1.dmp'', upload yes: ''CrashID=bp-77892e62-fc92-424a-976c-aa2bf2130213''
Wed Feb 13 21:19:28 2013 GMT: file ''/tmp/dumps/assert_20130213191923_1.dmp'', upload yes: ''CrashID=bp-4c01873b-72f5-4ba5-8eb2-26fea2130213''
Wed Feb 13 21:27:49 2013 GMT: file ''/tmp/dumps/assert_20130213192745_1.dmp'', upload yes: ''CrashID=bp-a938b0d8-1887-4e6d-8cb6-b3dd62130213''
Wed Feb 13 21:39:42 2013 GMT: file ''/tmp/dumps/assert_20130213193936_1.dmp'', upload yes: ''CrashID=bp-565ce966-ad7c-4a44-b225-f1a342130213''
Wed Feb 13 21:40:43 2013 GMT: file ''/tmp/dumps/assert_20130213194039_1.dmp'', upload yes: ''CrashID=bp-a07f2392-df55-47ce-933d-879852130213''

*does not recognize the video card

Davidw-valve thanks this was exactly my problem.
solved easily with the command

~ $ sudo apt-get install primus-lib:i386

Now I play all my games on maximum performance that my notebook can provide me with the latest drivers =)

Thank you, and for sure this topic will help others as well.