A couple of tips especially for older Macs. I have an old iBook G4 (MacOS X 10.4) that happily runs Opera 10.54 (it is even running Unite, and you can e.g look at my sharing of photos from Greece, see http://webserver.mrwalker.operaunite.com/photo_sharing/content/, i.e at least when the machine is actually ON…) and I can watch (sluggish) Flash and watch streaming on Norwegian Broadcasting (NRK), if I want. Which I don’t. But it works. If you want.
If you have Flash 10.0 working DO NOT “upgrade” to 10.1. This is even more sluggish and might break other software.
If you have Flip4Mac 2.2 working DO NOT “upgrade” to 2.3. It brings DRM and might even sneak install Silverlight. AND could break your favorite browser.
Hopefully these “technologies” will become obsolete and die in some very near future. Steve Jobs might be right after all…
If you own an old PPC machine I would also stay with Opera 10.54. I highly doubt these machines will run any subsequent Opera release on a satisfactory level.