Buyer rep agreements...

I am still fairly new to real estate and I have a question....how common are buyer rep agreements? Do most Realtors still use them? I have represented at least a dozen buyers in closed transactions the past year and a half or so (I know... I am pretty inexperienced ;-) ) and I have never once even thought about using one. I ask because I just had an old friend contact me: they are looking for a house, have a buyers rep agreement with a Realtor but are unhappy with him/her. They had no idea I was even here or a Realtor, they just found out and wanted to let me know that if they don't find a house before the agreement runs out, they will let me know so I can help them once the contract expires. Hopefully they will find their dream home and everything will go smoothly for them (no matter who their realtor is!). However, the phone call got me thinking about contracts with buyers. Just wondering if anyone else has input or thoughts about this topic. Hope everyone has a great weekend! TGI(almost)F!!!