Google launched the Google Custom Search Engine back on October 24, 2006. Soon after, I switched this site and personal blog to be powered by the Google CSE.
I can personally say, I love it. Not only do I use it several times a day, instead of going to Google and conducting a site command, it actually returns what I am looking for (at least most of the time). With the built in search features in Movable Type, it sorts search results by data and not by relevance. So I often find the built in search feature both a time waster and very slow to return results. The Google CSE works fast and accurately.
In addition to being a great way to find my content, it also has earned me some money. I have integrated it with my Google AdSense account and I have earned some nice pocket change on the side.
They have a great support staff in the Google Custom Search Google Groups discussion forum, to answer your questions also.
I am not the only one in love with the Google CSE. A DigitalPoint Forums thread has a few people praising Google over it.
I started a bit of a case study a few months ago and combined a Google co-op search engine with googlepages and am so far pleased with the results.
I've never set one up for money but I have used it for personal use and found it very easy to use.
Forum discussion at DigitalPoint Forums.

Comments:
Andru Edwards
05/16/2007 04:54 pm
I agree with most parts - Co-op is very cool, but it is lacking a couple of features that would really make it shine. The one that is most notable to me is the lack of sort options. It ONLY gives results by relevancy - but what if I want it sorted by date to make it easier for me to find something? If I write 40 articles a year on the iPod, and have been writing about iPods for 3 years, that is 120 articles I need to blindly sift through if I want the one from 2 months ago. I would LOVE to be able to sort by date or relevancy, similar to how Google News allows you to do it. Thoughts?
Barry Schwartz
05/16/2007 08:36 pm
That would be nice, I agree.
Panos
08/20/2007 07:54 am
Hi, I, ve been watching and experimenting coop since it started. I expexted it to be really huge but months later i realise that it didnt. Maybe if people used more often it could press google to make it better. I dont know why its not so well known, i find it very interesting. In order to help coop users i created a directory only for coop cse where ayone can submit freely either his direct coop cse link or his webpage if he has a cse implemented. Take a look at it coopdir.com