My beta experiences run the gamut from fabulous to dreadful, but I won't go into detail here.
There is light at the end of the tunnel though. I'm fortunate in that I found two fantastic beta readers who double as brainstorming partners and are also friends. (You both know who you are.)
It still baffles me that Karen has helped so many people and received so little thanks. She beta read for me and was not only fast but very insightful. (Cheers again, Karen!)