I've got about a hundred user apps, EVERYTHING is on my card, it's class 10, partitioned 1024 mb w/32 swap, and I'm using the native a2sd on PG's 0728. My phone's never been quicker. The card upgrade was a huge boost, and freeing up so much internal memory helps, too (I'm floating around 25 mb used.)
My biggest issues are with programs with lots of strain on the cpu. Angry birds has run like crap from the get go, The Weather Channel app crawls no matter what, and Opera's mem leak or whatever was/is wrong with it stops my phone dead. I've even unistalled ADW and Launcher Pro in favor of Zeam Launcher. It's lighter, and I love the scrolling dock.
All this added together means I can have over a hundred user apps, all external, and my phone is the fastest it's ever been.