Well, I tend to use a lot of +DSP plugs and sum things in my MIOs, so I'm not sure if thats "ITB" or not. Definitely "in A box" though. But in a 64 bit DAW, I find a lot of true ITB plugs and techniques work just fine, and I'm using that alone more and more these days. In fact, I've rarely used the Sontec at all in the past few months!
But I was replying to the UAD comments. While I find them truly amazing and wonderful for mixing, I don't use them nearly as much for mastering. Many of the coolest plugs there are great because they're so close to the originals... I've used and loved the old UREI LAs and Pultecs and Pultecalikes entirely for their glue and color, which UAD nails to the floor. But it's so close I'd just as soon use the real deal than a plug when needed, esp when it gives me an opportunity to use some other analog kit (already converted so...). More to the point, in most cases I'm not getting paid to add color, but shape a completed work that already has all the color the artist wants and producer intended. So I generally veer away from colored tools, instead adding those shades separate and apart from eq, dynamics etc. (+DSP has models called "character" that are non-linear, dynamic models of simple valve, FET, and transformer stages that can be inserted around a signal path).
Still, they're handy and quite great. I use them regularly in mixing, and they're useful in mastering too. They've done a really nice job in not making the analog goodness cartooney, like TRacks etc.
