The reason for trial products is to enable us to make purchase decisions, for example you get the chance to see if the product has the capabilities you need or that it is of the quality you want. If you are planning or have planned a project that requires flashbuilder and intend to release that project then you aren't really trialling anything you are actively using it for production development. So even if you did finish the project in 60 days on day 61 you should be sending a cheque to Adobe.
So Adobe gives you a choice, if flashbuilder suits your needs buy it, if you are not interested in paying for Flashbuilder but would like to develop nice Flex 4 swfs you use the open source SDK and an alternative free editor to write your code.
Just note these are my thoughts on the process, every EULA has different legalise but at the end of the day my interpretation is "If you want to use our product you have to pay for it".
Can one download a trial version for production if i can do it within the trial period? Or trial is only for learning purpose?
I want to download flash builder.
Cool, no support required then after 60days?
Go for it...
I think the real point is that Adobe want you to become a Flex developer after the 60 days is up, so the idea is that if you did complete some project in that time, you'll still need to buy a licence to support it properly after that time. I don't think there's a restriction, but I'm not a lawyer.
If you complete a project in Flex within 60 days and it's all good, then that's good for Adobe even if you don't buy a licence because every time you explain how it was built it helps Adobe to publicise that Flex is cool.
I really don't see how you can develop a good app in 60 days and not then buy a licence to follow through for the future though. If it's a bad app, who cares after 60 days!