There is indeed a limitation to the "flex compiler" that is included with CFMX. The limit is either 32k or 64k depending on who you ask. I cannot find (off hand) the actual MM document that describes the limit. The limit is to the amount of "compiled actionscript". It is affected by pretty much everything you do in the CFFORM tag. Even adding a style can cause a change in the size.
The leads to the unfortunate situation where you are refreshing a form over and over trying to get pixels to line up or a font to size correctly while you hurl epithets at the screen in frustration because of the uninformative error message:
Keep in mind that flash forms are useful in certain situations - a straightforward wizard, a couple of date boxes, a series of dropdowns etc. Macromedia has included the product to "wet your appetite" regarding the power of Flex. Flex is indeed impressive and worth examining as an option. Sad to say the price tag is simply too great and does not match the level of need in most cases.