I've used I-don't-know how many different cards wuth a realtek chip. They're perfectly acceptable for your average workstation, just as Conexant's Winmodem chip or generations of S3 chips make acceptable hardware.
However, I far, far, far prefer to buy brand name NICs (Intel, 3Com, Linksys, DLink, SMC). I've seen generic NICs - same as any other card with that chip, right? - do things that are kind of goofy compared to their name-brand counterparts, llike spike segment traffic on machines that aren't being used, for long-ish periods of time (a minute or so).
Not a comforting thing. How much are you saving over a $10 Dlink card?