I think that these points have been discussed at length in other threads.
My point is, does this break my employment contract. Does it render things like non-compete clauses void if i had to leave to a better paying job. And what else do i need to be aware of?
You cannot continue to work for months/years and then turn around some time in the future and say "my contract of employment was broken in early 2010, so these clauses are void". If you continue to work for the company under the amended conditions i.e. pay cuts, you will be deemed to have accepted the new conditions by your actions.
On a practical level, if you feel you can get a better offer elsewhere now and want to leave immediately, you could refuse the salary cut and essentially force your company to continue paying the original rate of pay or make you redundant.
One caveat on all this is collective bargaining agreements in unionised workforces. If the majority of employees are in the union and the union has agreed to the cuts, then your employer may be entitled to reduce your pay without your permission (even if you are not a union member yourself).
On non-compete clauses - check the exact wording of your contract. I once worked for a company that had extensive non-compete clauses in all contracts. However, in the resignation/termination part of the contract, there was a clause which said (to paraphrase) "this contract of employment can be terminated with 1 months notice in writing by either party". So when I resigned to move onto another job, the letter I gave when handing in my notice simply said "I wish to formally give 1 months notice that I wish to terminate my contract of employment with company X......I enjoyed working for the company.. thank you etc. etc. ". In this case, by terminating by contract of employment, it meant that the entire contract including ALL the clauses were terminated. I though this was a big oversight on the part of this employer, but it appears a very high percentage of employment contracts are written the same way. Sloppy drafting, but to the employees advantage.