Keep away from it, at least as long as they reference the SourceForge download site!
Edit 2: Since this answer in 2014, SourceForge has got new owners, who abandoned the adware bundling policy, but FileZilla, back then one of their first, major partners for adware, has still been distributed with adware bundles through other channels.
The FileZilla download from SourceForge (their official download site) definitely installs unwanted software without the user's explicit consent and knowledge (thus malware). It was NOT the software advertized in the SourceForge downloader popup, which I rejected.
I tried and first got an offer for a price search software, which I could reject. That was, of course, what I did. A few minutes after opening FileZilla, an "Optimizer Pro" window opened up, harassing me with reports about possible "optimizations" and asking me to register.
This software was never mentioned in any screen immediately visible, there was no pre-set checkbox, and even looking over the EULA quickly didn't show me anything suspicious.
This kind of malware - adware, spyware, browser hijackers (start page, search engines etc.) is becoming a growing pest, even from renowned sources (Oracle's Java runtime being a typical example for this). Just make these malware sites known! How long did it take for the browser toolbar crapware bundled with Java to be mentioned in public? SourceForge still seems to be a renowned site, but this can spoil their reputation very quickly!
-- some other alternatives have already been mentioned here.
I think the unwanted software might have been installed by a deceptive EULA page, as shown in this article:
I remember a similar EULA page, but with "FileZilla" instead of "CamStudio" in the title. It suggests an EULA for the desired software, the EULA itself looks pretty much standard (yes, I expected the tool to try make me install unwanted crapware, so I read into the EULA), only the fine print on the left (which I probably forgot) reveals than another, adware, not named there, is going to be installed by clicking "Accept".
The EULA page shown in the article is clearly deception: it is titled as an EULA for the desired software (CamStudio, FileZilla or whatever), and in a small printed side note, it adds something entirely different, not even naming the adware to be installed. This is the classic fine print trap, a traditional method of deception. Of course, most legal systems make such "contracts" void, so there's usually neither a legitimization to install unwanted software, nor any other valid commitment.