I've got three right now, 2 in my 150 gallon and one smaller one in my nano tank. The ones I have now are Yellow Faced Pike Blennies that come from the Caribbean. I also have a male and female Caribbean Sailfin Blenny in with them. Wasn't sure how that many tube Blennies would do together, but they all have found there own areas, and get along fine.
If you get one get some tubes for them to live in. I suggest you find some vacant coco worm tubes. PVC tubes work but doesn't look natural. What I do now is put the tubes in the quarantine tank and then just move the tube with the blenny into the display. If the fish is going straight to the display you can put the tube into the container your acclimating them in, in 30 minutes or so they will probably find there way into the tube. I've got a few threads on RC with pics and vids. Feel free to ask if you have any questions.
Yellow Face Displaying
http://www.reefcentral.com/forums/album.php?albumid=3269&pictureid=52326[IMG]
Orange Throat - from the Sea of Cortez
[IMG]http://www.reefcentral.com/forums/album.php?albumid=3269&pictureid=23373[IMG]
Caribbean Sailfin Blenny
[IMG]http://www.reefcentral.com/forums/album.php?albumid=3269&pictureid=52328[IMG]