Rear wheel sideways "play"

It really pays to UTFS.

I noticed yesterday when I picked up my bike to go outside, that there was a feeling of something moving - I always pick up a bike by the saddle and the h/bars.

Upon investigation, I noticed there was "play" at the rear wheel. I've never had that before. I could well be, as discussed above, that when I was using the degreaser, some went into the rear hub. Its quite a bit of play, but I'm hoping it lasts 3 days, then I'll take it to Vaidas - my first visit to his shop.

It wouldn't be from the degreaser, it would more likely be that when tightening the track nuts the cone nuts moved.
It can easily be fixed using two cone spanners (pictured above) and 1234's steps:

take the wheel out
make sure one cup and cone are locked nice and tightly together
put the wheel back in the frame and tighten up the axle nut on the tight cup and cone to hold the wheel in the frame so you can adjust the loose one accordingly
start with the loose cone, adjust it until there's no play in the wheel, then undo it just a fraction (when you tighten up the cones locknut it will compress the cone a tad), hold the cone in the same position with a spanner and tighten up the cones locknut, see if the wheel is nice and smooth then adjust if needs be (it might take a couple of go's)
tighten up the axle nut and go for a ride

But make sure to tighten that locknut up as hard as you can, and keep the cone spanner on the locknut to make sure it doesn't move when tightening up the track nut. My wheel's been perfect for the past 3 weeks since following the advice in this thread.