I'm curious about these, as I see them for sale. 

Are there any notable differences besides being yellow and coming with perhaps a strap?

I did find this rather intriguing poster of one of the water proof models. How successful were they underwater?  To me that seems rather gimmicky. Even if they were waterproof, why would I want to be listening to music while swimming?

Oh, and are the sports range collectable? 

To flagrantly plagiarise a post from the BBOX side of S2G....there's a walkman there??

I'd venture to say that these models were numerous and "plasticky". They never retained a lot of their value. The strap however may be very collectible. I'm sure less than 5% used their walkmans IN the water and probably tossed the belt away.

Still like Nak D said it would be nice if you could find a photo with the Walkman in the water...as I don't see any portable audio in the pic above

Whenever I see them, I'm struck by how big they look. Too big to be jogging with, or playing soccor or any sport really. 

I think they're great but the WM-F5 (in your pic) was by far the nicest (and smallest).  They aren't rare and the black ones are a treat.  The main problem I find is that they do develop the COD and are hard to open due to the plastic waterproof covers on the screws.

My brother use to have one, they worked well but the rubber seals tend to go particularly the ones around the headphone jacks which then made them susceptible leak.

Love the picture of Sharon Davies the British Olympic swimmer.

I still have two of them and a blur panasonic shockwave, using 5 daily at the moment as yet another iphone has packed up.

I'm a big fan of the Sports Models, there's something facinating about the color yellow and the instant recognition that it's a "Sports Model", check out some of the posts on here with some larger collections.  As with all models there's the bargain models and the higher end, the better ones would be at home on the beach or in the rain.  I've got a few with metal door latches that seem to be built to military specs that I love.  Sony and Panasonic perfected these units, although I think there's some really nice AIWA Models floating around. 

These do appear an issue at first: when fixing up my WM-75 I had to tease the covers off using a fine bladed knife, the carefully disassemble using decent screwdrivers as the screws were quite small.

I have a tiny sucker I made from a piece of 5mm petrol line hose which 'sucks' them clear.  Actually, this is pretty sad.

Actually that's pretty clever

Holy &*&%$ !!!! I never cared much for walkmans until now...wowee!!!

There not for going under water with

but on a rainy day or to the beach

sence there sealed it will keep the sand out

and can be rinsed off

probably good for dusty work place too

and kids spilling there soft drink on it.

The print advertisement sugguests that they are fully waterproof...misleading much?

I like the idea of a shockproof walkman, this would appeal to me. 

They might go underwater

but the main problem would be getting a

good water seal at the phone plug

so the original phones should be used.

I think you'll find the biggest problem is using headphones under water, not a pleasant experience for either ear or headphone.