Of course it all depends. Personally, I have had no problem starting with Lift even though I’d only used Scala in the REPL before and just for some toying around to get to know the syntax.
It certainly helps a lot if you already know how to use collections in a functional way without explicit loops, so you can read and understand other people’s code more easily. But basically, I’d say it is doable learning both Lift and Scala at the same time even without a background in functional languages. It’s just the collections thing you’ll have to get used to and if you happen to know Ruby (or a language with list comprehensions) you’ll easily understand it.
The Frothy integration has not yet been updated to the newest version of Lift and I don’t know of any site which actually uses it but maybe this is a thing to ask on the Lift mailing list. In any case, I think Frothy only helps you connecting a Lift setup with some Cappuccino frontend but does not provide many wrappers to the Objective-J code, so you’ll still have to write code in Objective-J.
At that point you can ask yourself: Why not write the whole thing with Cappuccino and decide afterwards if Lift integration is actually needed.
Considering Lift alone: You certainly can use Lift with some UI Kit like JQuery UI for the visuals. Lift has many advanced possibilities which make it possible to build complicated web applications but you’ll have to care about the wiring for the visuals yourself.
(And arguably, a stateful, non-MVC (‘view first’) framework like Lift might be better suited for a rich internet application than a pure MVC framework…)
