If I leave monitor mode on after exiting aircrack-ng without turning it back off, does it slow down my internet?

Can you give the output of:

sudo lshw -C network; lsb_release -a; uname -a; sudo rfkill list

Do you connect via wired or wireless and do you dual boot the system?

*-network
       description: Ethernet interface
       product: AR8152 v1.1 Fast Ethernet
       vendor: Atheros Communications Inc.
       physical id: 0
       bus info: pci@0000:01:00.0
       logical name: eth0
       version: c1
       serial: 1c:75:08:3b:f3:4d
       capacity: 100Mbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vpd bus_master cap_list
ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=atl1c
driverversion=1.0.1.0-NAPI firmware=N/A latency=0 link=no
multicast=yes port=twisted pair
       resources: irq:46 memory:97000000-9703ffff ioport:5000(size=128)
  *-network
       description: Wireless interface
       product: Centrino Wireless-N 1000
       vendor: Intel Corporation
       physical id: 0
       bus info: pci@0000:02:00.0
       logical name: wlan0
       version: 00
       serial: 00:26:c7:b7:a3:b8
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list ethernet
physical wireless
       configuration: broadcast=yes driver=iwlwifi
driverversion=3.2.0-26-generic-pae firmware=39.31.5.1 build 35138
ip=192.168.2.103 latency=0 link=yes multicast=yes wireless=IEEE
802.11bgn
       resources: irq:43 memory:96000000-96001fff
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 12.04 LTS
Release: 12.04
Codename: precise
Linux Serenity-AOD255 3.2.0-26-generic-pae #41-Ubuntu SMP Thu Jun 14
16:45:14 UTC 2012 i686 i686 i386 GNU/Linux
0: acer-wireless: Wireless LAN
 Soft blocked: no
 Hard blocked: no
1: phy0: Wireless LAN
 Soft blocked: no
 Hard blocked: no

On 7/2/12, actionparsnip <email address hidden> wrote:
> Your question #202001 on Ubuntu changed:
> https://answers.launchpad.net/ubuntu/+question/202001
>
> Status: Open => Needs information
>
> actionparsnip requested more information:
> Can you give the output of:
>
> sudo lshw -C network; lsb_release -a; uname -a; sudo rfkill list
>
> Do you connect via wired or wireless and do you dual boot the system?
>
> --
> To answer this request for more information, you can either reply to
> this email or enter your reply at the following page:
> https://answers.launchpad.net/ubuntu/+question/202001
>
> You received this question notification because you asked the question.
>

Wireless and I don't know what "dual boot" is.

On 7/3/12, angel diaz <email address hidden> wrote:
> *-network
> description: Ethernet interface
> product: AR8152 v1.1 Fast Ethernet
> vendor: Atheros Communications Inc.
> physical id: 0
> bus info: pci@0000:01:00.0
> logical name: eth0
> version: c1
> serial: 1c:75:08:3b:f3:4d
> capacity: 100Mbit/s
> width: 64 bits
> clock: 33MHz
> capabilities: pm msi pciexpress vpd bus_master cap_list
> ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd autonegotiation
> configuration: autonegotiation=on broadcast=yes driver=atl1c
> driverversion=1.0.1.0-NAPI firmware=N/A latency=0 link=no
> multicast=yes port=twisted pair
> resources: irq:46 memory:97000000-9703ffff ioport:5000(size=128)
> *-network
> description: Wireless interface
> product: Centrino Wireless-N 1000
> vendor: Intel Corporation
> physical id: 0
> bus info: pci@0000:02:00.0
> logical name: wlan0
> version: 00
> serial: 00:26:c7:b7:a3:b8
> width: 64 bits
> clock: 33MHz
> capabilities: pm msi pciexpress bus_master cap_list ethernet
> physical wireless
> configuration: broadcast=yes driver=iwlwifi
> driverversion=3.2.0-26-generic-pae firmware=39.31.5.1 build 35138
> ip=192.168.2.103 latency=0 link=yes multicast=yes wireless=IEEE
> 802.11bgn
> resources: irq:43 memory:96000000-96001fff
> No LSB modules are available.
> Distributor ID: Ubuntu
> Description: Ubuntu 12.04 LTS
> Release: 12.04
> Codename: precise
> Linux Serenity-AOD255 3.2.0-26-generic-pae #41-Ubuntu SMP Thu Jun 14
> 16:45:14 UTC 2012 i686 i686 i386 GNU/Linux
> 0: acer-wireless: Wireless LAN
> Soft blocked: no
> Hard blocked: no
> 1: phy0: Wireless LAN
> Soft blocked: no
> Hard blocked: no
>
>
> On 7/2/12, actionparsnip <email address hidden> wrote:
>> Your question #202001 on Ubuntu changed:
>> https://answers.launchpad.net/ubuntu/+question/202001
>>
>> Status: Open => Needs information
>>
>> actionparsnip requested more information:
>> Can you give the output of:
>>
>> sudo lshw -C network; lsb_release -a; uname -a; sudo rfkill list
>>
>> Do you connect via wired or wireless and do you dual boot the system?
>>
>> --
>> To answer this request for more information, you can either reply to
>> this email or enter your reply at the following page:
>> https://answers.launchpad.net/ubuntu/+question/202001
>>
>> You received this question notification because you asked the question.
>>
>

I recommend you disable the n speed in the wifi. It's a known issue with centrino wifi. You can do this with:

echo "options iwlwifi 11n_disable=1" | sudo tee /etc/modprobe.d/disable-n.conf > /dev/null

reboot to test