I've decided to use SilverStripe 3 for a medium-sized project I'm currently working on, mainly because I've read ModelAdmin got a face lift.
Even though I've developed a lot of sites with older SS versions, I find 3.0 nice but unbearable. It's been a walk through hell to tell you frankly. Bugs are numerous, documentation is lacking, in many cases I end up browsing through source code and there's way too much magic used there. My forum posts remain mostly unanswered and that's also often the case with other people's questions here I stumbled on while googling. Almost no existing modules are supported in 3.0, too.
Perhaps my impression would be similar with 2.4 since I've never used SilverStripe for anything more complex than a website with some custom pages and now am building a simple, but not DEAD simple CRM system, I don't really know.
I had good experience with SilverStripe in the past and am grateful for all the hard work put by its team into it. But releasing 3.0 in the state it was fails all the trust I had in this project. I cannot rely on a software that releases beta-quality code as a major revision and I'll have to put a lot of unneccessary work to iron out all the bugs for my customer. It really kills all the time gains I get from - really nice in concept - scaffolding mechanisms, etc.
To summarize, I do not recommend using 3.0 for anything more complex right now. 3.0.1 does fix some bugs, but the CMS is still unstable and slow. Having browsed through a large part of SS code I also got impression that it's become too complex for quite a simple tasks it should be doing and frankly lost hope that it'll get really fixed any time soon. Perhaps with time it'll get to its former glory (I wish SS devs all the best with that), but we do have to use something in the meantime.
Sorry if that sounds like an ungrateful rant, but I hope it might save someone from going the 3.0 path that I went and makes people responsible for release schedules think more before they call 3.1 or whatever next major version will be "ready".