Pretty much everyone knows that a PC performs at its best with a fresh clean install. 
Give it a few months of everyday use and it’ll not take long until the boot time increases until it comes to the point where one can boil the kettle while waiting for the PC/Laptop to finish booting up.
Back at the beginning of October, I built a nice Core i5 based system and wanted just one thing - a responsive PC with my everyday tasks that doesn’t slow down after several months. So I decided on the Agility 60GB for the OS and redirected my desktop, documents folder and e-mail profiles to a 2TB WD RE4-GP, which I also use for data.
3 months later, I currently have around 50 applications installed, consisting of various audio, video and graphics utilities not to mention many updates over the months. As a fan of open source and free software, I also have a quite a large folder on the SSD with about 100 folders of portable freeware applications. I know by this stage, if I had a hard disk in my PC, the boot time would probably have reached at least 60 seconds at this stage for the desktop to appear, not to mention the 30 or so seconds for the OS to settle down. This also takes into account things like periodic defragging, clean-ups and disabling startup processes. That was my experience with Windows XP and now I’ve Windows 7, which while not as resource intensive as Vista, it is still is more demanding on disk activity than XP.
So after 3 months of everyday use without the usual maintenance I would have done when I had a hard disk, how long do you reckon it now takes to boot Windows 7 and launch 15 applications?
Have a look here: 
Note: Video opens in a new window
Seen videos showing faster boots than mines?
Sure, you’ll find hundreds of videos on YouTube showing multiple scripted launches, faster boots and so on, but that’s not the point I’m trying to show here! It’s not about shaving 1 to 2 seconds off application launches. What it is however, is having a very responsive PC that doesn’t require all the maintainence hard disks need just to keep the PC responsive as the months go by.
To give an example, I’ve seen someone with a pretty good specification PC (Intel Quad Core Q6600, 3GB RAM, 500GB HDD and so on) and this person took pretty good care of his PC, installing just what he needed. It had Windows Vista as its OS and after just a year of every day use, the PC boot time reached 2.5 minutes before anything could be launched and even after that, it took 60 seconds just to launch Firefox! Periodic disk defragging did little to help and eventually this person bought Windows 7 and did a clean install. Only time will tell if this issue repeats.
Finally, I’m sure the most common reason people avoid SSDs is the cost.
To make an SSD purchase more affordable, try thinking about these with your next PC build/upgrade: 
[ul]
[li]PSU - Do you really need a PSU larger than 450 watts? Most PCs without more than 1 graphics card will generally not use more than 400 watts at peak. If you have a <$/€100 graphics card, your PC may max out at 250 watts, even with multiple hard disks and optical drives. My i5 750 based PC with the entry ATi HD4350 uses as little as 47 watts idle and maxes out at just under 200 watts going by my watt meter.
[/li][li]Graphics - Any modern entry level add-on graphics card can handle Full HD video acceleration, yes, even thouse under €50! If you’re not a gamer, do you really need such a fancy graphics card? Tip: If you’re not sure, get an entry-level card and if the time comes when you find that you’re using some fancy animation software that requires a higher end card, then buy one. By that time, the price will have come down or maybe even a newer model will be out than what you originally debated about.
[/li][li]Case - If you don’t intend competing with your friends on a fancy case, don’t go for more than you need. I couldn’t be happier with my Antec Three Hundred and it’s no noiser than higher end cases I’ve seen people with.
[/li][li]Blu-ray writer - Unless you have a Blu-ray disc player and want to create Blu-ray discs, consider a BD-ROM instead. Two 1TB+ hard disks (1 as backup) have a cheaper cost per gigabyte than most blank Blu-ray media.
[/li][li]RAM - Do you really need fancy high end RAM?
[/li][/ul]
Add up the savings and use them towards an SSD purchase. You may even have some change left over. 
On the other hand, I admit that I do enjoy trying out all sorts of audio/video/web editing utilities I come across, which is I’m sure the main reason my PC use to slow down so much so quickly.