A few important notes about the SE:
1. Many older SE models only have 800K drives. You'll need an Apple-branded floppy drive (aka one from the late 80s or 90s) if you want to use Apple's system disks from their older software section or some of the shareware/freeware/public domain programs available for it on the web. USB floppy drives don't read or write to 800K disks, just 1.4MB disks.
2. Macintosh SEs marked "FDHD" or "SuperDrive" under their name CAN read 1.4MB disks, so a USB floppy drive will work fine.
3. You can run up to System 7.5.5 on an SE, but you'll need the full 4MB RAM to do so.
4. It's not dangerous to go inside an SE as long as you know what you're doing. Avoid touching the anode cap (which looks like a red suction cup) on the CRT and you'll be fine. (The SE generally self-discharges this as long as the machine is unplugged, but I'd still avoid it unless you must replace the CRT, and even then you can discharge it). What is tricky is actually getting inside the case--you need a long-shafted Torx T15 screwdriver to do so. Sears is hit-or-miss for finding these but you can usually find one online if you look hard enough.
5. Beware of bad capacitors and leaked batteries. Pre-1989 SEs had their PRAM battery soldered to the logic board, which many did not care to clip when it went bad. Capacitors are a problem in the majority of old Macs; re-capping the board is usually a good idea regardless of its condition--the caps will fail sooner or later.
6. I'd recommend picking up an SE if you can get one at a low cost or for free. Prices on eBay are inflated and shipping is usually quite high. These little computers are fun to play with and serve as a reminder of how much we could do with so little years ago. Aside from some of our online uses, most of the basic uses a typical user has for their computer have remained the same from the time these computers were introduced in 1987 to today. I will also mention that they can be surprisingly useful today--I used one productively to help children learn last fall. (I used it alongside several iMac G3s with Kid Works 2 and for differentiated instruction for individual students in mathematics).
7. The introduction and discontinuation dates given earlier in this thread are for the SE/30, the SE's more powerful cousin. The SE itself was introduced in March 1987. It was revised in August 1989 to include SuperDrives. Apple officially lists its termination date as October 1990, but SEs were produced into February 1991. There were a few minor revisions along the line--original SEs shipped with noisy drum fans, often called a "rat cage" or "squirrel cage", but were replaced by blade fans sometime around the beginning of 1988 (which were quieter and didn't cause screen interference). Earlier models with a 1.4MB drive were labeled as "FDHD", with later models branded as "SuperDrive". There were also a few technical revisions to RAM jumpers and battery holder mechanisms.
8. The European models had different designations written on the front depending on their configuration, with RAM and hard drive size written in an x/y format (i.e. an SE with 1MB RAM and a 20MB hard drive was marked as a "Macintosh SE 1/20").
