I have upgraded RAM from 1GB to 2.5GB on my laptop. The obvious difference i have noticed is system is more responsive. But there isn't any difference in booting time.

Please let me know which functions will be boosted by this upgrade? Thanks

Booting is done mostly from hard drive, getting things loaded into memory. The more memory you have, the less 'swapping' back and forth to disk your system has to do, so it'll be more responsive.

For reducing booting time, you can try to reduce the number of services. Boot time also depends on the strategy used by your distro. Fedora 10 uses plymouth and is going to be better on this.

It depends on where the bottleneck is. If RAM was the issue then more ram helps balance things out until you peak out other resources. Like the cpu, or I/O rates of the graphics cards or hard drives.

More RAM generally does not help boot time. But if you're running some sort of encrypted filesystem, I suppose it could. More RAM helps with other processes, like running 2,000 instances of a web browser. Or converting large chunks of data, such as video encoding. Or playing some media types that would otherwise require a lot of I/O, which can be buffered into RAM to smooth out the playback. You can also allocate a ramdisk so data that is accessed at lot can be stored in ram and therefor have a much quicker I/O rate. And otherwise lessen the wear and tear of your harddrive(s). And should you have buggy software, more ram can increase the time it takes for windows to reach the BSOD.