Thanks for clearing up the meanings of the columns, but what kind of value does "current" mean? For example, it says the current value for "Reallocated Sectors Count" on the faulty drive is 58, while, according to raw data (and the hover-over text) it's 613. Also, it says it's 253 for an other drive, and that has no problems.

EDIT
Here's an other screen capture.
OK, I'll start backing up important data (mostly save games - I reinstalled Windows a few days ago, so nothing important on that partition yet) and keep doing tests.

Before that I would suggest to run MHDD. Bad sectors are "hard to read sectors" or "sectors with long access time". By running tests sometime they could go back to normal as they could be created by bad transport or long inactivity of HDD (shop storage etc).

That's a guess but it's probably because attribute count vs relocated sector count is not 1:1. So when disc is good - attribute value is say 255. Than bad sectors appear. Hdd counts relocated sectors and every 10 relocated sectors it decreases value of an attribute.

Wiki

Count of reallocated sectors. When the hard drive finds a read/write/verification error, it marks that sector as "reallocated" and transfers data to a special reserved area (spare area). This process is also known as remapping, and reallocated sectors are called "remaps". The raw value normally represents a count of the bad sectors that have been found and remapped. Thus, the higher the attribute value, the more sectors the drive has had to reallocate. This allows a drive with bad sectors to continue operation, however, a drive which has had any reallocations at all is significantly more likely fail in the near future.[12] While primarily used as a metric of the life-expectancy of the drive, this number also affects performance. As the count of reallocated sectors increases, the read/write speed tends to become worse because the drive head is forced to seek to the reserved area whenever a remap is accessed. A workaround which will preserve drive speed at the expense of capacity is to create a disk partition over the region which contains remaps and instruct the operating system to not use that partition.

Thanks for the wiki link, but I knew about that; what baffles me is the seeming inconsistency of the attribute among my drives, that it doesn't show its value as the current value, and that Reallocated Sectors Count should be lower on the good drive.

Current/Worst/Threshold are SMART settings and they differ from drive to drive. What you are interested in are raw values - on good drive there should be 0 (zero) here.

Ah, thanks, that cleared it up. I didn't know they were relative values.

Yes, and attribute value should be 255. I also assume when you have small drive every (an example only) 10 bad sectors attribute value goes -1 and if you have big drive it takes 50 relocated sectors to decrease attribute value by one. Why it drops from 255 to 0 and not increases from 0 to 255 ? Don't have any idea. Maybe it has sth to do with that 'sparse' place where bad sectors are relocated?

Thanks everyone. Now, whose answer should I mark as solution? I'm leaning towards Lexor, but you all have been very helpful, so I have a hard time deciding...

raw data is the actual numerical data (ex: how many times a sector was reallocated)

The data displayed in current, worst, and threshhold is normalized data. They take the raw data and based on it calculate such values. The exact math they use differs between attributes and manufacturers.
wise manufacturers would normalize it linearly to a number between 0 and 100, effectively making it a percent.
Most values on my intel SSD for example are normalized in such a manner.

This all makes it very difficult to read. The important point is to replace a drive which has values which exceed the warning thresholds. Your drive throws a smart warning and thus should be replaced.

I strongly disagree with luxor's suggestion of trying to fix bad sectors via software. It's not effective and not worth your time, effort, and data. Drives are dirt cheap nowadays and data is too valuable to risk.

If you do not know the cause of fail sectors you cant make proper verdict.
I would still say, try to repair it once and test after. If problem occurs again - throw it out.
I repaired my disc and still have zero bad sectors after 2 years from fixing.

Oh, you have a lot to lose. You stand to lose everything that you wrote to disk between the time you backed up and the time the disk failed.

There is no repair you can perform, not without a remanufacturing facility. All you can do is remap all the bad blocks you can find at present. That's not any kind of repair, because more will turn up, or the drive will go full-on failure.

Not worth it for a 250GB disk.

Not if you do extended tests after as I said.

By repair I mean not only remapping but also just testing bad blocks if they are bad for real or just somehow badly demagnetized due to some reasons thus showing bad / long access time.

My disk after repair has zero reallocted sectors.

Then you are very fortunate. I've been maintaining computers for a long time, and my experience is that once a disk starts showing bad blocks, it will go into complete failure soon after.