It is / would it be possible to run 64bit programs on OSx86? This includes the question: Do we need it? Which programs make use of the 64bit bus width?

Not at the moment. You would have to wait for a newer release from the OSx"86" community that will support 64-bit apps in the near future.

To be perfectly honest I think the majority of us have no real need for 64-bit ... well, not just yet.

Do you remember last years WWDC keynote? Steve Jobs had a 32 and 64-bit version of a demo app that he was showing off. Both were simultaneously loading in a 4GB photo of the Congress library. The 32-bit version had to swap out to disk and was getting bogged down; the 64-bit version didn't even blink. It did a filter in 28 seconds that took 84 seconds with the 32-bit version. This is a really good example of how 64-bit can help us, but to be honest, how many of us are going to be throwing around 4GB image files in the foreseeable future? For now, casual users aren't really hitting the limits of 32-bit, but in a couple of years I'm sure the landscape will change and we'll be doing just that, but for now 64-bit is really a requirement for the Pro-App/Scientific industry.

This is not to say that I don't want or need 64-bit right now -- I do :-)

i would need it too....
i work with maya alot, all the easy stuff i do in osx, but when it comes to heavy projects, i must use vista x64.....

But this only works if there's enough RAM. If you have 'only' 2 GB the 64bit version has to swap too.

That's correct. In order to really utilise 64-bit you're going to need a ton of ram. However, with more and more of today's towers accommodating 16Gb ram, 4Gb ram would be the minimum and 8Gb would be the sweet spot.

Edit: I forgot to add that the latest Mac Pros can accommodate 32Gb ram!!!

Side Effects's Houddini is exclusive to 64 bit so yeah....
http://www.sidefx.com/index.php?opti...021&Itemid=270

Not true. 64bit capability is useful for a lot of things other than accessing >4GB memory. Like being able to do arithmetic on 64bit integers directly instead of splitting them up into cumbersome 32-bit operations. Or load/store 64bit qwords atomically (useful for a lot of things, obvious example is OS X kernel's own timing routines which have to do some quite messy and slow math, with lock-free access but still needing to loop back if one of the 32bit dword changed while we were doing our messy 64bit calculation.. and so on). And 64bit architecture gives you tons of new 64bit registers. An optimizing compiler will be able to make better use of those extra registers (unlike x86 where you only have like 5-6 registers to play with), resulting in faster compiled code.

All that said, most current programs are not 64bit, and if they are, they typically do not take full advantage of all these new features. Things will change (soon) but for now, 64bit is still not a big deal (specially for running leopard, kernel is still 32bit binary with only bits of 64bit routines, even though it allows you to run 64bit userspace apps). So you're not losing much now.