Yes & No
It is problem because many people are comfortable researching things they are interested in on the net. So in places where the internet is available, I could see it possibly deterring some from joining. However, there is a 'digital divide'. People not familiar with the net or who have limited access obviously can't utilize it. Additionally, I think that for the most part the WTS has pretty good influence over current members. People who grew up in the faith or converted years ago probably are not likely to go "asking questions" at any higher rate simply because the net is there. Considering all of the places on the earth that have limited internet access (i.e. developing nations), it is likely that WT growth in these countries will continue to grow no matter what kind of technology is around.
I believe the Watchtowers biggest problem would be people who share their theology and beliefs (to some degree) rather than those that reject them."Apostates" on the internet pose a very little threat to the organization imo. People will continue to leave, as they always have (just as people will continue to join). I think the big danger for the WTS is if one day members begin to get frustrated and want reform within the group, with the possibility for fragment groups to form facilitated through digital communication.