I think there is a bit of a problem in the way most people talk about low end cards. The words "poor" or "weak" or "slow" come up too much. Really these things are inappropriate and I think the 9400gt has had a bit of a rough ride with public opinion.
The problem is that the 9400gt is part of the nVidia 9 series, a very recent line of cards, but it is at the bottom of the line. This means that you are getting a newer card than any of the 8 series and the newest compatibility features etc. but it will not outmatch cards like the 8800gt in performance because that was at the top of the 8 series.
So, does that mean the 9400gt is a slow, poor, weak card? Not at all, it just isn't the fastest. It is however, a modern direct x 10 card capable of resolutions as high as 25600X1600 and designed to run Vista's fancy bits with an extra kick.
It is also capable as a gaming card, if not state of the art. It will not run Crysis perfectly above Low but it is playable on Medium. Bioshock runs well on full but slows down occasionally. With slightly older games, the 9400gt works perfectly. Doom 3, Half Life 2 + episodes, Far Cry. All games that were state of the art upon release and this card will run them all at maximum with a dual core processor and a couple of GBs of RAM.
This card also has excellent DVD, HD-DVD and BluRay acceleration. If you wish to watch movies on your computer then this machine will do the job well for a decent price.
All in all, this card isn't a muscle machine but it will play most games with the settings tweaked at least and will fit most uses except bleeding edge gaming.
A final note, if using this card its performance increases dramatically with the latest drivers (as do most cards.)