Yes, I believe websites work. They are cheap enough now that cost ought not be a consideration for most people, unless you get into a lot of e-commerce or complex programming and maintenance. If you're wanting to put up a site advertising your company, listing services, showing before/after pics, and allowing a potential customer to request an estimate online, you should be able to fit that into even the most frugal advertising budget.
The reason I beleive they work is that more and more people are spending more and more time online, and online is EASY. I often see webpage listing on the sides of vehicles, and will look up those that interest me or are for services for which I have a need. Bottom line, it makes it more convenient on the customer to look you up, and allows you a pretty much unlimited forum to sell your services. You can tell a customer how nice their home/deck/driveway/fence/whatever will look after it is cleaned, but a picture SHOWS them how clean it can get. Heck, Beth has offered to do a webpage for folks here for $250.00, if I recall. That's CHEAP, and she obviously does great work. The registration and hosting costs are cheap now too, so there's really no reason not to.