The market of connectivity/website monitoring is very saturated at the moment, and it has been in this state for at least a couple of years. I spent several weeks on the market research for a very similar service and here is a snapshot of my bookmarks from that time:
http://i37.tinypic.com/2n6651g.png
This is just a subset of existing services, all of these are functional and useful. They target different users and have different pricing levels, but quite a few are actually free and there was two free services with over than 50 sensor points each. Some are simple, some are very (overly) comprehensive. Some are very aggressive marketed (Pingdom), some are low profile, but still sit at the top of respective Google searches.
So, in short :) - this makes sense as a hobby project, but trying to carve out a non-trivial market segment for it is going to be the challenge. The technical and design merit alone is not enough, it will come down to marketing, sales, support and knowing how exactly you want to position the service ("the bigger view"). Make sure you can justify the effort before committing to it. I know I couldn't.