False success rates. Xrumer has a lot more bugs than you think. For example, it will report captcha successfully decoded (particularly recaptcha) but in reality, it has not solved it at all and so the registration has failed. The only way to verify this is to go to Debug mode and check one by one. The message you get when you're registering is inaccurate in a great number of cases.
There is no way in hell Xrumer will be able to beat a service like Deathbycaptcha, because DBC is specialized to captcha solving OCR (that's all they do) PLUS they have human solvers for those captchas which the OCR did not solve. Xrumer cannot solve captchas for which captcha DLLs haven't been created. Therefore, if you get platform X which has its own captcha format captcha X, and DLL X has not been created by Botmaster, there is no way in hell Xrumer will be able to decode it. Xrumer isn't some amazing intelligent robot which can read like a human and decode any text you put in front of it. External services such as captchabot and DBC, on the other hand, can tackle almost any type of captcha you put in front of it. I'm not sure if captchabot uses human solvers, but if not, that means their OCR is freaking awesome.
There is massive, massive room for improvement in captcha solving OCR from baseline of Xrumer. This is, perhaps, where Sweetfunny could really get one up on Botmaster. But, unfortunately, most users would not see it this way, because Xrumer reports so many false successes that you THINK your registration/post has succeeded when in fact it stopped at the captcha (even with 100% correct xmessages).
