IMO, she once received a lot of hate for being a slamless No. 1. But, she's really not in tennis fans' general frame of mind anymore, so it's really not an ongoing thing. This thread made me realize how long it's been since we had any substantive discussion about Safina.
As to why she was considered by some to be the "worst No.1," It was based less on that fact that she didn't actually win one (like Woz or Jankovic), but how she repeatedly had meltdowns in Slam finals after playing high level tennis to get there.
In a way, it's a backhanded compliment -- we expected more from her, so it was more disappointing that she never won. Safina had big weapons, unlike Jankovic and Woz, and I think we forget how incredible she could play and blow people off the court. Sort of like Davenport.
I think when people say "worst No. 1" many people actually mean "most disappointing No. 1." As pointed out, based on the stats (weeks at No. 1, number of Slam finals), she's hardly the worst.