Should you throw out every single fan that uses sleeve bearings? No. Should you never ever buy a heatsink with sleeve bearings? That's up to you. With proper lubrication sleeve bearings will provide performance and service on par with that of their ball bearing counterparts. If left alone for a long time, and run at higher temperatures they will fail before the ball bearings will. With some fans using both bearing systems the lines become blurred...

For things like powersupplies it makes much more sense to only use ball bearing based fans. For CPU coolers that are on for extended periods of the time the same goes. For the average home PC which is on intermittently, sleeve bearings are a fine choice. For overclockers running Peltiers, ball bearings should be the only kind of fan considered. That said the decision truely depends upon the circumstances, and the quality of the fan being considered.

For my sleeve bearing fans I think I'll go put a small dab of grease under that sticker just to be on the safe side ;-)