My BB 0.4 experience:
I tried running BB 0.4 for a couple of weeks. The same day I installed BB I got the itch to try overclocking so I went big and tried Chevyno1 1.2Ghz ULV. Much to my surprise it ran flawlessly, well almost. 2 days later I got an application to force close. Nothing major, but I'm not willing so sacrifice stability for performance. I figured it was my kernel so I downgraded to 1.1GHz. After a day I also had another force close. Down to 1Ghz, same thing after a couple of days. I also began to notice that the BB toolkit would always force close. Lowered to 800mhz ULV and the BB toolkit problem went away. When the new version of Quandrant came out, it would force close during the benchmark! So I downgraded to 800mhz LV and then 800mhz MV. Finally it would work. But still I would get some force closes every day or so. One more thing, very occasionally the touch screen would become unresponsive. I would have to press the screen multiple times to get it to register. To be fair to BB, I didn't give the stock kernel much of a chance.
My Lithium mod experience:
I saw that Jrummy was conspiring with other devs to make the Lithium Mod, I knew I had to give it a try. First thing I noticed (other than a new launcher), was my battery life is easily 50% if not 100% better. Previously I was having to charge after 12 hours, now it is more like 24 hours. Funny that the kernel didn't seem to make a difference in battery life. I've only been running Lithium since yesterday, but I've noticed no force closes and no touch screen issues. This time I'm going to stick with the stock kernel a week to get a baseline of performance and stability. The quadrant scores aren't any higher (and may actually be lower than BB). However, the responsiveness seems better. This is worth more than any quadrant score (although it was fun to get a higher benchmark score than the nexus one 2.2+)