> I will hit 0 on the numeric keypad and it takes a very long time before it starts to render anything.
This excerpt from "Memory & Multiprocessing" may address your issue:
"Important: You may experience a small delay when the background processes start for the first time. A message in the Info panel indicates when the background processes are initializing. Deselecting Render Multiple Frame Simultaneously stops the background processes; reselecting the option causes the same delay when you close the dialog box."
> How can I improve my rendering time?
Also, it's crucial that you install the After Effects CS4 (9.0.2) update. That update fixed a lot of performance issues.
That's not normal. Previewed frames disappearing wopuld point to a more serious problem. What memory settings do you use exactly? Do you use the disk cache? Do you use OpenGL? If so, what graphics card, screen resolution etc.? What footages and effects do you use? As a minor, verify that you have the latest update as Todd suggested, for everything else provide more details.
I am using an Nvidia geforce 285(latest drivers) Screen resolution is 1600x1280 I believe, but I may be wrong because I am not at home. I have the lastest updates for AE. I have set up a disk cache on a seperate drive. I have been using hvd shot at 24p using keylight and some dv25 footage shot at 24p with simple cc. If I start a preview and it starts rendering frames and then I click on the timeline to stop the render, sometimes the green bar goes away or is tramendously minimized.
HDV and DV captured through Premiere? For such formats, check the Media Cache. Several of the compressed formats are conformed/ indexed, storing auxiliary data to that folder. If it gets corrupted or the folder is simply full, it can seriously mess up things, especially in AE. Defining a differnt location for the folder may already help, as the default is your user home directory, which already is the busiest folder on all your system (beside the Windows and Program Files folders)...