You will see a huge difference in speeds. My MAC boot up time has reduced quite a bit - the wheel spins 1.5 times I think, and Im booted!
Also, while using the drive, you'll notice applications open MUCH faster, and are just more generally responsive overall.
A word of advice though - you cannot ever defrag a SSD. It will reduce its performance. Data on a SSD in a MAC is written throughout all the blocks. As you add data its written to the 'end' block, whether you have deleted some space or not. When the drive reaches the last blocks, its goes back to the blocks where data was previously marked as deleted.
When data is deleted from a SSD, the blocks are only marked as deleted, they are not actually cleared for new data. As a result, when you wish to write new data to those blocks, the drive needs to clear the data and then write the new data to it.
As a result of this, SSD drives are known to 'slow down' over time, depending on how much you have used it.
This is where a feature known as TRIM comes into play. When the system is idle, the drive will clean itself up without you even knowing. Hence it will delete the data from the blocks marked as 'deleted' previously. This means those blocks are now free from any data and can be written to very quickly - just like when it was new.
Windows 7 supports TRIM. BUT the OS X DOES NOT.......yet!
Bear with me here......
When you buy your SSD, you will either get an older SSD with an 'Indilinx' controller, or the newer (and more expensive) SSDs will have the 'SANDFORCE' controller.
Make sure you buy a SSD with the SANDFORCE controller!
What this newer controller does is it 'TRIMs' on-the-fly. The OS does not need to support TRIM. So when the drive is idle it will clean itself up, and remain fast.
For example, I have had my drive for several months now. When I apply a large update, for example, I notice the system is a little slow - just like running from a 7200rpm HDD. However, after a few hours I notice its back up to high SSD speed - I believe this is after the drive has reorganised its data, and TRIM'd itself.
As you correctly pointed out - I have a 240GB Vertex 2 SSD - and its been just as fast as day 1. Trust me, you'll notice the system is much more nippier.
The OWC Mercury Extreme is another Sandforce based SSD which is also known to be very highly recommended.
Another word of advice - do not try to clone your current disc across. Its always better to re-install from scratch when upgrading to a SSD. I did clone across since my MAC was pretty new and I didnt have that much on it at all, but apparently its still always better to reinstall from new so the SSD has its blocks written to sequentially.
I made a couple of Youtube videos showing the difference in speed.
This is the first video which shows the install and original speed differences.....
After making that video, after a day or so, I noticed the drive had suddenly got even faster. I think this was after the drive had settled in, and its on-the-fly TRIM'ing had kicked in to reorganise the disc etc.........
Hope that helps