I was not aware of that but this a little informative:
It is not really helpful for Bible study per se. It is helpful for comparative literature reasons. In other words, it can be helpful for looking up how words are used in other bodies of classical literature. You have access to the Liddell-Scott lexicon. You can access the Symth classical grammar which being old still is fairly standard in scholarship. You can access the Vulgate and click on words to get their morphologies if you're big into Latin. In other words, Perseus is not really a Bible study site, but it can be used to increase your knowledge of the Greek language and grammar and maybe even just some of the thought world of ancient times.
Here is a link to the the material that Perseus hosts http://www.perseus.tufts.edu/hopper/...on:Greco-Roman
If what you want to do is track down words or citations from BDAG or Kittel you can do this via Perseus rather easily as long as Perseus has the source. Perseus is not housing the Loeb Classical Library online. However, they do have many of the older Loebs online. They do not have every single Greek (or Roman author), but they do have many of the major ones. This would not replace a university/seminary library, but it can help ease the pain if you move far away from one. Generally if you're looking something up from BDAG or Kittel they will give you a line or book reference to the Greek work. All you would do is follow this up through Perseus. If you're looking for every Greek work written, you'd have to move away from Perseus and start eyeing the TLG (http://www.tlg.uci.edu/) but now you're talking big time money. - Michael Hanel; http://www.bibleworks.com/forums/showthread.php?1157-Using-Perseus-in-Bible-Study
There are a lot of good references out there to assist with exegesis. Obviously, Strong's is a tremendous source, though the dictionary is rather abbreviated (thus using with Perseus and their references to LSJ). But, honestly, I have to be careful when using online sources.
For example, Blue Letter Bible is a good reference; however, I would hesitate to recommend it to my fellow Catholics as the commentary is deeply flawed (from my perspective, of course). For example, the in-depth Lexicon they use for Greek is Thayer. Joseph Thayer was, as far as I understand, a Unitarian and I have, over the years, seen examples where that has infiltrated his definitions. Much of the commentary on the site seems to me (and your mileage may vary) a bit "Scofield-ish." (e.g., dispensationalist). Obviously, as a Catholic, I'm neither a fan of Darby nor of dispensationalism (not trying to offend you with those statements if you are).
That's what I see with a lot of the online sources. They are useful for scans ("Where does it say that, again?"), but I am very careful when looking at many of the in-depth "Bible dictionaries" or "Critical Lexicons".