the Sempron's are not "garbage" at all
in reality, you won't notice any difference between it and an Athlon 64 unless you actually do use 64-bit applications, and currently there aren't any
for about a 2% performance difference, people say that a Celeron 2.8 is "crap" compared to a Pentium 4 2.8, and that a Sempron 2800+ is "crap" compared to an Athlon XP or Athlon 64 2800+
for 99% of people, the difference is nothing
now I'm not saying at all that you should not get an Athlon 64 2800+ or 3000+, I'm just saying that a Sempron or Celeron will still do you fine