Recently, I received a call from a man who'd taken my card at a wedding our band played two years ago. He was calling because his son had recently gotten engaged and he wanted to book our band for the affair. He explained that he'd taken our card and made some notes on it at that event and that was why he was calling us. He then read us the notes he'd jotted down at that affair:
jazzy, talented, low volume, creative, leibidikThis is a great idea. I'd like to suggest that if you're at an affair and you're enjoying the music, then take the band's card and jot down what about their performance you liked. Keeping a file of these cards will help to ensure that you remember (and consider) them when you are planning your own simcha!
In the past, I've recommended that people take a note of bands that are playing too loudly and refrain from patronizing them. If you're at an event where the band is particularly bad -- and we've all been at such events -- by all means take note of that as well. In that case, though, it's unethical to ask the band for their card.