I've been using them for ages, I only use them as an alternative to allofmp3.com though. I find allofmp3.com has more songs, is better to navigate and also has on the fly encoding with lossless codecs. Every now and then mp3search.ru has something allod doesn't so I use that too, although this one has most of it's tracks as 192mp3's but it does have 99% of it's tracks for ten cents. I also love how, on both sites you can go back and redownload any of your previously bought tracks if you need to.
I've been using mp3search since February now and it's been 100% reliable, I paid in $50 using my credit card for paying in $50 I received a $10 bonus, of this I still have $51.30 in my account. I really didn't consider for a second about any security risk about using my credit card, personally I have a very blaisay (how on earth do you spell that?) attitude to my credit card purchases as Visa will cover the cost of any fraudsters that screw you over. So your safe to use them as far as I can see. I you need any more info just check out there forums
http://www.mp3talks.com/index.php? loads of people on there have been using it for years. If you don't wanna go for it then do check out allofmp3.com this is a much, much bigger and more wellknown site which also exploits said loophole, it's 100% legit in that they won't rip you off and have even been given the nod by the BBC who investigated the site when it started to get bigger publicity when the Records Association of American tried to get them shut down.
The only thing i'm worried about is that Russian copyright law changes. If this happens then the site would get closed down (because it currently exploits a loophole) and at the rate I download songs i'm just hoping I don't get stuck with credit it my account if the site ever gets closed down.