I used CrystalDiskInfo to analyze my HDDs as I had the suspicion not everything's right with one of them (a 250 GB Samsung SATA HDD which is divided into two partitions, one for WinXP and one which I install games on). It seems my suspicions were correct: it shows the health meter of that drive is "caution" (yellow), and, looking at the detailed S.M.A.R.T. results, it says that the source of the problem is that the values for "Reallocated Sectors Count" and "Current Pending Sector Count" are too high.
Now, I understand what these mean, and I also see how many of them there are (613 and 2, respectively), but I don't get what exactly three of the columns in the S.M.A.R.T. results section mean. Specifically, "Current", "Worst" and "Threshold". For example, it's 50/50/10 for "Reallocated Sectors Count" and 100/100/0 for "Current Pending Sector Count", while they are 253/253/63 and 253/253/0 on an other HDD which is apparently in perfectly good condition (no reported errors whatsoever). Could someone shed some light on their meaning for me?
Also, how serious do you think is the threat of my HDD acting up soon, based on these problems?

Observe this Relocated Sector Attribute. If that is new disc - it could contain some bad sectors that will be relocated to the 'sparse' area of HDD and that will end the case. But if you will notice steady drop of that attribute, which means that more and more sectors are damaged - prepare for HDD malfunction. Use free Victoria 4.46b for tests of your drive. It a very good tool - it gives you SMART but also can scan entire drive for 'quality' of each sector.

Also if the disk is new or there are not important / backuped data on it, you can try to repair it. There is one nice prog called MHDD to do this, but use it only if you are experienced PC user and know what you are doing - in other case you can lost your HDD :P I did repair one of my HDDs myself and its fine since that time (it was 2 years ago). This program (among very big amount of other options) can do tests of "faulty" sectors if they are really bad or not. Of course it will test other sectors as well.

Whenever you see a SMART warning that's a tip to make sure that you're data is backed up. This warning isn't likely to be of much consequence provided that it isn't increasing very quickly.

Google did a HDD study a while back and found that the failure rate of disks with a SMART warning was 10x the failure rate of ones which hadn't been flagged.

Basically just something to keep in mind. They also found that brand and price didn't matter over all, although sometimes there are bad batches produced.

It's definitely not a new disc, I've had it for some years now (not sure how many, but at least three).

Can you do screenshot of CDI data?

But did you check it with SMART before?

Sure, if I knew what that is ;-).
You mean such data as firmware, serial number, interface, etc.? No, it was the first time. (I have a bad tendency of not checking something if it functions properly...)

More important are attributes.

Anyway you can do something like this.So you do not have comparison as it was at start.

Check the links in the response to this post. Seems to be the same question and the response had several links about SMART interpretation.

So this attribute could be changed a while ago. I would backup and observe for a month giving this disc some extended weekly tests with Victoria. BTW did that Crystal Disc gave you some TEC(failure) date?

OK, here goes...
No, or at least I didn't notice anything like that.

Current: The current value of this attribute for the drive
Worst: The worst value ever recorded for this attribute for the drive.
Threshhold: A predetermined value, if current value exceeds it you get a smart warning that the drive is about to fail.

Worst only applies to a few attributes, for example reallocation sector count has no purpose for "worst" since worst is, by definition, the same as current for that attribute.

You should backup your data and replace the drive as soon as it throws a smart error. your drive has been giving you trouble and seems to have a lot of defective sectors (which were then reallocated) so you should back stuff up asap, buy a new drive, and throw this one in the trash.

Can you expand the window to show attributes below?

Also. As tburger said, I would run CDI everyday from now on, and compare all numbers if they are changing or not.

Again: backup, observe, do some weekly test. If atributes will remain on steady level - you do not have to worry.