Yeah... I can see myself using the M570 somewhere where there would be either no desk space almost at all for moving the mouse with my laptop (like a cramped airplane?). or if it was some glass surface where my mouse doesn't work and I don't have a mouse mat with me, and I felt using the laptop's trackpad isn't good enough.

But if you can comfortably use a mouse (both the space considerations and your hand), I feel there's not much point to use a trackball instead of a mouse. It doesn't give you any extra advantage in games or anything like that. I use a mouse (instead of a trackball) even from my couch nowadays, as the mouse actually works fine against the flat armrest of my sofa. Heck it works fine even against a firm pillow.

Also when talking about hand conditions, I feel for many a mouse is actually more comfortable than a (thumb) trackball. I presume if you had e.g. rheumatoid arthritis or somesuch which makes your fingers, especially your thumb, less nimble and flexible, moving and flexing your thumb or other fingers with a trackball takes more effort than moving your whole hand/arm (to move a mouse).

I can't say I regret buying the M570, it is a nice backup for me, but for reasons or another I've been just using it very little.

Mouse > trackball > trackpad > gamepad (for aiming, desktop use, FPS gaming etc.). So I feel trackball is definitely better than a trackpad on laptops, but not as good as mice.

Do the emulated old arcade games (like Tempest and Marble Madness) on PC support trackballs?
If so, it would be worth buying one just for those.

Using one A LOT when working offshore. Trying to do something with conventional mouse while vessel is rolling is an mission. And no, trackball is not less precise than mouse; all you need is a bit of practice. The only problem that I see here is while trackballs are pretty susceptible to "ouch-I-can't-work-there-is-something-under-my-balls" ailment, at the same time they tend to be pretty effective dust and dirt collecting devices, even in well maintained work environment. Other than that, the could be an almost perfect substitute for a mouse.

But I still prefers an ordinary mouse. For me just more natural to move your hand to move your pointer, than moving just a thumb to do the same.

Pros:
- It's way faster, more natural kind of moving the pointer around (you'll notice that when you are forced to use a mouse again)
- More precise (yes, this needs a few days of training, but it's worth it)
- You don't need a mousepad (like every week I mean...)

Cons:
- It's rather hard to find a good trackball, have a look at logitech ones, don't see any other real contender

Slightly off-topic, but: If you do any kind of heavy graphics work/image editing I highly recommend you try out an actual graphics tablet. ( The input device, not a tablet PC. ) Even a fairly cheap one is still much more efficient and natural than working with a mouse ( or trackball/ touch-pad etc. ). Once you get used to working with one, you'll never look back.

I've used both and as people have pointed out the better ones aren't made anymore. Logitech should really upgrade their marble mouse.
http://www.amazon.com/Logitech-Optical-Marble-Mouse-USB/dp/B00005T406

Does anyone know where you can buy spare balls for the various trackballs?
It's a pity that more games aren't optomised towards tablets benefits like absolute mode.

One nice advantage of that and trackballs is that up is always up.

Hmm, I've actually had the opposite experience for image editing and GIS work, and found that the trackball was more responsive to small movements than the mouse, and led to more onscreen precision. (For example, tracing a property boundary along a meandering stream to create a polygon.)

I should add that I use the standard variety with the central ball, not the ball-under-the thumb variety. The central type are handedness-neutral.

In MAME, yes the do. This is what started me using trackballs over 15 years ago, playing Missile Command, Centipede and other such games. Once I became accustomed to them I never wanted to use a mouse again. I do image tracing and other image editing fairly often, I have no problem doing that with a trackball as opposed to a mouse. I had been using hoarded (and long discontinued) Microsoft or [url=http://www.amazon.com/Microsoft-TrackBall-Optical-PC-MAC/dp/B00005853X/ref=pd_sim_sbs_147_5?ie=UTF8&dpID=410QW4Q0WAL&dpSrc=sims&preST=_AC_UL160_SR160%2C160_&refRID=1PNW2A8XNZPVBBAN65CK]X08-70386 Optical Trackballs up until my last X08-70386 failed last year. Luckily I happened upon the Logitech M570, less than $28 delivered from Amazon. It has proven to be a very capable and excellent replacement.

At work I use an old D68-00007 that I found laying around and no one else wanted, and really enjoy it - and it has the bonus that no one else can use my computer because they don't know what to do when faced with something that's neither a mouse nor a trackpad.

Thank you for that information. I remember I had a trackball for my Amiga 1200 and successfully used it on the Brilliance art program. I must admit though, it was the size and shape of a house brick.

Yep, those trackballs work well for image editing. Thumb trackballs aren't quite as good.

I found this recently.
http://www.gamingtrackball.com/pages/overview

A company is trying to get a new trackball launched that looks a lot better than the current offerings.
It is only at the initial stages and they have a funding page here.
https://www.indiegogo.com/projects/gameball-the-gaming-trackball#/