at my previous agency - it was 3 months. Originally was 1 month, but i managed to secure a 33% payrise on the threat of leaving (it was a total bluff - I showed them the job spec of the roll I applied for - they thought it was a full contract outlining my new job role & they panicked - they never read the paperwork). They called it, but they offered a payrise (took me from £30 -> £45k) - on the hit of increasing notice from 1 -> 3.
I went from a Senior Desktop support Analyst to Helpdesk Manager - The job title, i felt, was worth the notice period sacrifice. (each to their own) - was made redundant about a year later =P
This opened the door for my current role. Service Desk Manager. Hands on managerial. I want to leave but cant because of the notice period (again, increased to 3 months). As above - I was made redundant out of previous agency - took a 35k (10k paycut). on my 6months probation, in my "congrats your about to pass your probation with flying colour" review, i said Im resigning because im responsible for too much without the adequate compensation (literally took over the entire running of the IT infrastructure & abuser, despite having a network/infrastructure manager already in place. Again, same as before, they offered me the payrise but I had to take the increase in notice period.
Each to their own gents. You point a gun at your manager / the company - expect them to point one back at you
Going to post my story in here one day =P it would be a funny read.
All im going to say is have the attitude of being known for "G.S.D" - it will get you noticed, you will get rewarded, if it doesnt its an excellent CV builder