Reading this topic reinforces my decision to buy a hydraulic lift. I do my work on a gravel driveway using jack stands sitting on 2x12s but the older I get, the more cautious I get. Plus it would be nicer (and faster) to raise and I like the idea of sliding around on a wheeled chair or creeper.
In researching lifts, I landed on a product called "MaxJax". It's a half-lift (48 inches or so), and is unique in that the posts are removable and the pump is on wheels so you can move everything out of the way when you are not using it. Uses 110v instead of 220v. It also has an optional attachment for motorcycles. Check it out:
http://www.maxjaxusa.com/features.html
Alot of discussion on the Garage Journal Forum:
http://www.garagejournal.com/forum/index.php
Near as I can tell, the best prices are from Northern Tool (about $2,000 delivered). Costco also carries them. In my case, I will have to pour a concrete pad for another $400 or so.
I was considering a fixed, full-height lift for around $1500, but I like the removability and use of 110v (since I don't have 220 in my barn).