i took this last friday with the cheap tubes, completely straight from camera except adding the border and a resize for web.
to be honest, for the price im not bothered by the fact they're fully manual and with manually closing down the apeture. i find the image adequetly bright at f5.6 (which is what i took this at, i think, with the smallest of the extension tubes) although working at anything smaller for a moving target is fairly useless. static object you can open up to compose and focus, and close down when you need to shoot (im using nikon)
focusing wise i didnt have much of a problem, but for something moving like this ladybird its best to blast off a series of shots rather than try to frame up one, i was at high iso (1000) so was particularly being careful about shutter speeds. it didnt need more than 3 or 4 frames to get a pin sharp one, and out of the 20 or so shots i took (limited by a card capacity) i got a few that are useable.
ive not used the tubes more than 2 or 3 times since i got them, they just sit in my bag waiting. but to be honest if you've got good camera technique it shouldnt be a problem and for me im not willing to shed out more for something im not using regularly. yeah its a bit of a hassle to use them, but you can still get pretty good shots.
i realise this might not be too helpful for canon users, but i thought id still give my opinion for any nikon users.
edit: i think mine were £4 on ebay