I don't have the details with me, but yes, they still do 30 day passes. Basically, they last 30 days and you can use them a certain number of times. There are also One Day and Three Day tourist passes which you can use as many times as you like within that period. To answer your other question, we were in Bangkok at the weekend researching our new Bangkok Guidebook and we had first hand experience of that problem. Our Skycard (the one you can keep refilling) had expired. All they did was transfer the amount left on the old card to a new one.

Thanks for your questions. We will add them to our new Sky Train section over the weekend:

http://www.bangkokguidebook.com/transport/skytrain

The skytrain
 

Do they still offer discount on the skytrain tickets if you use it more than 30x in a month?

If you buy the prepaid passes do they expire after a certain amount of time, thus you losing what you have paid for?

10 trips = THB 250
20 trips = THB 300
30 trips = THB 540

all types are valid for 30 days