Using 了, 到 and 过

Yesterday's class was marginally better than the last few, as I finally feel like I've grasped some of the complexities of grammar. We focussed much of the class on when to use了 (le), 到 (dao) and 过 (guo). Here's how I understand it (and please correct me if I am wrong!).

过 (guo)
To be used in sentences to which you can apply the "have you ever" test, with no specific point in time reference. For example:

你吃过北京烤鸭吗？
ni chi guo Bei Jing kao ya ma?
Have you (ever) eaten Beijing roast duck (before)?

你看过这个电影吗？
ni kan guo zhe ge dian ying ma?
Have you (ever) seen this film (before)?

我没去过中国。
wo mei qu guo zhong guo.
I have never been to China.

了 (le)
To be used for recent past actions with a specific point of time reference or when the status of something has changed. For example:

昨天晚上我吃了北京烤鸭。
zuo tian wan shang wo chi le bei jing kao ya.
Last night I ate Beijing roast duck.

今天天气冷了
Jin tian tian qi leng le
Today the weather has gotten cold

But not to be used if something hasn't happened. For example

昨天晚上我没吃北京烤鸭。
zuo tian wan shang wo mei chi bei jing kao ya.

And then there's my nemesis... 到 (dao) and 了 (le)
To be used when explaining the result of an action. For example:

Action:
我找玛丽
wo zhao Ma Li
I look for Mary

Question:
你找到玛丽了吗？
Did you find Mary?

Result:
我找到了玛丽
wo zhao dao Ma Li le
I found Mary

Action:
我去书店买一本书。
wo qu shu dian mai yi ben shu
I go to the book shop to buy a book

Question
你买到一本书了吗？
ni mai dao yi ben shu le ma?
Did you buy a book?

Result
我买到了一本书
wo mai dao le yi ben shu
I bought a book

So Mandarin speakers out there... have I got it right?!