What about the performance enhancement when using an SSD as the main disk?

I think that access times, rather than transfer rates, are the more useful feature of SSD's.

That's certainly one massive improvement. Yes, the random-access time on my current and past SSDs have both been around 0.2ms. I upgraded from a fast mechanical disk (WD Raptor) and the boot-up on the SSD just blew me away. It does so much, so fast.

Of course ureadahead and other tools aim to make the boot-up as linear as possible (they essentially write a whole load of files that are needed at boot into one sequential block) but that's where the SSD's second benefit comes in: huge maximum-throughput speeds.

The sustainable transfer speed of my first SSD (OCZ Agility) was around 200MB/s. My new SSD (OCZ Revodrive - a PCI-E card) tops out at around 540MB/s. The Revodrive X2 reaches somewhere around 750MB/s. There are solutions that scrape 2GB/s but they're prohibitively expensive for most people.

Like your plans, I started with my entire home being bind-mounted onto a RAID array on mechanical disks. This was good and is technically much more secure but it does limit the ability for the computer to really fly.

Browsers and other database heavy applications (feed readers, email apps, etc) need fast access to the disk to work well. You might want to weigh up how valuable your data really is, and if some of it can perhaps stay on the SSD and survive with the occasional backup.

Keeping various often-accessed files (like the Firefox database or gnome settings) on multiple mechanical disks is also pretty noisy. I have quiet, fairly slow disks and even I find it annoying when loading something causes 4 disks to start clunking away (I have 4-way RAID5). Perhaps this is something that you learn to appreciate after living with a silent SSD for a while.

These days the only things that are on the RAID are users' documents. That is ~/Documents, ~/Music, ~/Photos, ~/Vidoes and (for disk space reasons more than anything) ~/.wine. Everything else either gets an occasional backup (Firefox/F-Spot/etc SQLite3 databases once a day). I try to run a monthly proper ~/ backup (excluding the stuff that is on RAID) once a month, but I'm yet to cron it.

This is a good compromise for me. I get a lightning fast computer and all my really important data is quite safe and all my semi-important data gets backed up regularly.

Speeds up boot and application launch significantly. I keep my main /home on it as well and mount the bulk storage elsewhere so that when I'm not using it, that disk can spin down.

My setup is an SSD for / and a spinning disk for /home and it's great for boot time, installation of packages, and launch time of applications.

I detailed my set up here for a similar question.