I clean them when I decide to lubricate them. I usually end up with bad luck though when cleaning / lubing them. For the record, I used to never actually clean it. I started out with WD40ing my cubes, then I read some stuff online about how bad it was, bought some silicone spray and it worked great. I never have done a full out soap and water clean. I used to only clean it with just a paper towel wiping off the cube dust on the inside (and removing hair, etc). Now I usually wet the paper towel with water just to make cleaning it a bit easier.
I used to only spray some CRC into an edge and work it in (storebought cubes). I tried the disassemble and spray sweep one time, ended up getting dried silicone on my CS tiles and hated it, then haven't sprayed like that in quite awhile, until the other night.
This Type A / Type B hybrid I'm using has seen it's days, and I've only had it a few months. I started out lubing it only with an edge spray and work it in. Then I went to Florida, got sand in my cube (don't ever take your good cubes out onto a beach unless you really want to end up cleaning it out often), and had to clean it out. I decided to try out some Jig A Loo since I was going to have to buy more of something (why not get something I haven't tried?). I usually just sprayed it into an edge, work it in. It quickly made a lot of cube dust. I thought everything was going to be good then, but man it just felt not fast, but at least it felt smooth and I really think it helped round out the edges of the pieces inside the cube. Since Florida (in december) I hadn't cleaned it again until last Thursday. I decided to try a disassemble and sweep spray and man it worked wonders, until I was letting a guy scramble it for me and then it popped and it went all over the garage floor. The cube ended up real dirty, felt like it did in Florida, so I decided to clean and lube up last night, same method, but a bit more lube to see what would happen, and my overall opinion is that I sprayed too much and only after really working it hard last night and today (a lot of furious scrambling) that it got nice and smooth. What I like about this is that it's not real fast (like my girlfriend's storebought that I lubed, it's real quick), but it's nice and smooth and has little resistance.
I also noticed that the cleaner my cube is (well more like the less resistant it is to turn a face) that the fewer times it pops. Is that a mental thing or just how it is?