regarding the write time, Intel has claimed that the X-25 80 GB version will last for 5 years, assuming you deleted and rewrote 100 GB each day. That's much more data than an average user will use each and every day and in 5 years you'll want to get a newer and faster SSD anyway.
Even if it is exaggerated by 5x, 20 GB each and every day is a lot. As long as you don't like... reinstall Windows everyday and move off your paging files you should be fine. Even if you don't move off your paging files, if you're considering an SSD, you are either a labtop user, or you're an enthusiast desktop user who will probably put in 6-8 GB of RAM anyway... so the paging file won't be used that much.
Even if Intel exaggerated by 100x, and it would only last 5 full years if you only did a full 1 GB of writes each day (something you might expect from a "power-user" who installs lots of games, downloads and deletes a lot of movies, and spends a lot of time in general doing stuff on the compter), 5 years is still a good amount of time. I doubt that you'll see it last less than 2 years, because that's how long the first generation SSDs were lasting when put into a server.
Hint: don't RAID SSDs. Last time I checked, TRIM doesn't behave properly when RAID'd. That was part of the issue with the first-generation SSDs when put in servers. They weren't playing nicely. This was 2 years ago, about, however, so that may be very wrong today.
I really think that getting a 40 GB SSD is the way to go. You can get them for well under $150 and you'll realized most of the benefit (put your OS, your 1-3 of your favorite games on it, along with a few small applications like Chrome/Firefox). The major reason to bump up to 80 GB is just so you can install more games on it (: (3-5, easily).
A big thing to do if you do get an SSD + normal hard drives is to make sure you set up some symbolic drives changing your C:\Users\___ folders onto your D drive. There is a windows utility to do it (forgot what it was), you can also setup the sym links by hand, if you're not afraid of the command prompt. Finally, you can use Stardock's Tweak7, It's under the "Profile Location" section and it'll move any and all existing files for you too.
You may not need to move the AppData\Local or Roaming folders onto your D drive. They typically don't get THAT large and they'll give a slight performance boost to all your applications, whether or not they are on your C drive. (AppData is like a persistent "cache" for programs, allowing them to quickly load low-level information on startup. Things like Cookies and your web history for your web browser would typically live in AppData).