Jihn: Lightroom 4.1 RC2 solved some issues but added more.I find it frustrating to have paid for a product that was not ready for production use. Over all it has been a very disappointing two months since I got LR4 and I still have now now idea when it will be reliable.
There are quite a number of people having problems with LR4. It is much slower than LR3.6 for them with jerky mouse movement and slow rendering of previews. Many of us have gone back to 3.6 to wait until a 4.x version without crippling bugs is available.