'Global' Sim Cards? Good/Bad/Indifferent?

[Ianatlarge]

I travel a bit around SEA and to Europe and Australia. I tend to carry with me half a dozen sim cards. Not a major problem, but it can be annoying juggling these around and keeping them straight. I have read about 'global' sim cards, cards which work in a wide variety of countries. What I need is phone coverage and internet 2g or 3g.

Has anyone here had experience with these global sims? Do they work, fair price, reliable, any problems/pitfalls?

Thanks for any advice given.