I haven't used mine for portraits but wouldn't say it is ideal. 55mm end will be long enough on crop bodies but at f5.6 it isn't really going to give you the shallow depth of field you might like to isolate the subject from the background. A 50mm f1.8 would do a better job, although still not the very best option.
If you do get a 18-55mm make sure you get a version with VR.
Personally I'll either replace mine with something like the Sigma 17-50mm f2.8 or Nikkor 18-140mm. Before that though I'll probably get a Tokina 11-16mm or similar for landscapes and I already have 35mm 1.8, 50mm 1.8 and 55mm 2.8 macro which cover the 18-55 mid to longer end well and do a better job.