Well that all depends on who you ask. Ceramics are generally better bearings and will last longer if maintained properly. They are smoother, and will free-up the overall drivetrain a little. Don't expect to replace the bearings with ceramics and immediately pick up time on the track, it won't happen, unless you had a real bearing issue to begin with.
You have two specific places you can use Ceramics, the drivetrain (diffs & pulleys) and the wheel hubs. I use the Acer ceramics all around except, but I don't use them on the outer wheel bearing on all four corners since they suffer the most damage from impacts. You don't normally gain anything buy using ceramics on the steering posts or inside the diffs.
As for all bearings, Ceramics will only last if you take care of them. The Acer bearing's have a lightweight oil in them, not grease like most normal bearings. This means that after 1-2 weeks, you must clean, inspect, and re-oil.
If you want to save a little money, buy from AvidRC.com and mix and match Ceramics and normal bearings. Buy the outer diff bearings (front/rear) and the layshaft/spur gear bearings, a total of 6x ceramics. The ceramic's go for $5.00 each. Also buy about 30x normal wheel bearings at $1.00 each. This will only cost you a total of $60.00 for 36x bearings, about 18 more bearings than you'll get in a kit, while saving you $30.00.