While bike spam is scary, you need to look at your meta.
For example, there are something like 10 regular 40k players at my FLGS. Among these, there are 2 mechanized necrons, and 2 IG with a lot of tanks. So I'm not expecting our eldar players to spam to many bikes since they are much less powerful against these lists. But, if your meta is infantry or light vehicle based you can expect to see much more bikes.
Many suggest have been made to deal with them and they are all valid. I'm personnally planning to drown them in poison if they run MSU or to overload them with charging units if they are running larger squad. Reavers or Grotesques reaching them will mean they are dead.