We have been using Nokia IP 530's and IP330's for just over year now. For the most part, we have had very little problems with the Nokia box and their OS. Any of the real headache problems has been with CheckPoint application. The one area to watch out for is the guidbedit utility, we made manual edits, then when we went to upgrade, we couldn't, because we manually edited the objects.C file. We had to manually recreate everything.
There are some good scripts to automate some of the admin task on these boxes.