I use XAF for internal projects at the company where I work, and to be honest from my experience I find that as a framework, it covers 95+% of typical business scenarios with ease straight out of the box, - we use it as the main MIS system driving the business with c100 users across multiple applications both Win & Web
I'd agree, though, like any framework, the tradeoff is twofold - 1) learning curve which can be steep & 2) maintenance/upgrade of older versions as the framework itself evolves.
Both these, though, to my mind are endemic in any piece of software that needs to evolve, and come down to the tradeoff between learning the framework vs the time to roll your own solution, but personally I know given the time deadlines in most projects, I couldn't produce a solution that offers the same flexibility to end users as XAF in the same timeframe
I've been a XAF customer/consumer for the past 4+ years, and I'd be the first to admit that at the outset the learning curve was quite steep, and hindered by documentation that could have been better, but in the intervening releases this is something which has only improved, and whenever I couldn't fathom something, I can't fault, DevExpress support for both timely and informative responses.
Don't get me wrong - this is not meant to be a sycophantic rant about XAF as the ultimate tool you'll ever need, as I'm well aware of it's shortcomings, but with a little knowledge of the framework you can work through (around?) most of these for most line of business apps which I work on