If you intend to semi-regularly visit the free online virus scan pages, I'd advise against it: - malware can cause quite a few problems as soon as it gets onto your system.
If you're intending to use AVG or Clamwin or other free antivirus program, then go right ahead: it's a lot better than nothing, although often not quite as good as the paid-for antivirus products (of which I recommend NOD32)