I posted this in another thread, but looks like Logic 9 has a larger memory footprint then Logic 8. My empty template in LP8 uses 0.7 GB less of Logic's virtual memory then LP9. You can check this by opening the "Empty" project template in LP8 and then in LP9... once the template is loaded just check the Virtual Memory in Activity Monitor.
So if you were crashing in LP8 due to Logic's virtual memory hitting 4GB, it's going to be hitting that limit even sooner now in Logic 9. Until Logic is a 64-bit app, this will continue happening.
I've been hoping for this 64-bit update for some time now, barely getting by with big projects in LP8. Now that LP9 has come without a 64-bit version, I'm really hoping that a 64-bit update will come along side Snow Leopard, but I'm not holding my breath. The last big code change Apple did to Logic was back when they coded it for Intel... not only did they charge for that update, but it was long overdue.
One workaround that I've been using in LP8 (will work with LP9 as well) is by freezing tracks - sort of. This will only help those of you that load lots of EXS instruments. EXS IS able to load into RAM outside of Logic, but from my experience this doesn't happen until you load a certain amount of EXS samples... that is loading the initial EXS instruments doesn't load them outside of Logic's memory like the new Kontakt 3.5 does. So the first bit of EXS will actually contribute to increasing Logic's virtual memory.
Anyhow, if you've got a template and you're using lots of EXS, but for this session you don't plan on using the Strings that are loaded, then click the freeze button on the instruments you don't plan on using for this project, and hit the space bar immediately followed by "command-*period*". Logic will start and then stop the freeze, thus creating very small freeze files for the tracks (~4KB). Logic will now see these tracks as frozen. Save the project, and then re-open it... Logic will NOT load the semi-frozen tracks into memory because it thinks they're frozen... and so you'll have some extra RAM. Of course if you want to use the frozen track, clicking the freeze button off will force Logic to load the samples.
If you use this template often, by doing a save-as or whatever, simply copy the 4KB freeze files to the "Freeze Files" folder of the new project. Of course you can always just take the EXS instance out as well... but I don't do this cause I might eventually want to grab the frozen instrument quickly.