Mounting directly to concrete?

Definitely just frame out a small area to attach the TV mount to wood. While I can't say that something specifically bad would happen, for the little amount of $ and extra time it's better to avoid the potential risk of damaging the foundation wall.

An alternative is to install some blocking between your joists and use a ceiling mount for plasmas if that works with your joist configuration.

How thick is the poured concrete foundation? 8-10"?
If so, do not hesitate to anchor directly to it. Even if only 6" thick, the tapcons probably only have a 2" embedment requirement. I would urge you to secure to the foundation wall (en lieu of framing) if you are thinking tilting swiveling mount. The foundation will see so much less vibration and movement than a wood framed wall. The 1/4" tapcons (go with the hex head, so much easier to drive) will hold quite a bit of weight and will perform really well when installed properly.

Why would she object? Get all the rowdy boys downstairs and she can have the whole upstairs for her Tupperware party, what's not to like? ^)

I had a similiar issue in my house, i live in some older housing with concrete walls. I went to home depot and talked with the Hilti rep on site and he said to use there wall mounts. they basically had a bolt with a sleeve and then a nut on the end you tighten. they were rated for over 500lbs of pull out weight when used in concrete, per bolt. i used 6, 3 on each end of my mount.

i have this mount with a 60in tv and its performed awesome.
http://www.thinkvp.com/products16-19/X-LargeExtendMountVEX

here is a picture of the anchors i used.
http://www.homedepot.com/h_d1/N-5yc1v/R-100325224/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=hilti+anchors&storeId=10051

depending on the thickness of the bolt, you get more strength. i would recommend these because they were rated for pull out strength vs just hanging strength.

good luck!