Services is one of those great features that came over from NeXT. And as timsey says, will become more powerful as developers get used to their functionality.
There was a good article about them at
www.macedition.com that expalins their power. It's also like simx says, it is one of those features that requires a selection (from text, to a file, etc) otherwise they're greyed out.
They're especially useful if you can remember all the key combos. Suddenly, typing a word in a paper, wondering if there is a better synonym, highlighting it (shift + <- , I think?), then key combo alt + shift + = and OmniDictionary quickly returns definition and synonym. Quick, fast, painless, and every freaking app doesn't have to have it's own space hogging dictionary, every app can use it.
There's a lot of that 'object model' being overlooked right now as we move from OS 9< to OS X, but one of the coolest things of NeXT was it's idea of an object being a self-contained app or service that any other program could access. Almost like the Photoshop plugin model, but it was system wide.
Every app could use the same spelling dictionary, find and replace tools, font panels, color panels, ...etc. The cool thing about it was, not only was there consistency across the OS, but if you loaded a new app that added advanced features to the font panel, it could provide that to all other programs.
In the days that I was running a NeXTstation, developers were actually starting to write and offer 'engines' instead of apps. I don;t know what became of it (I lost track after I moved on from NeXT), but you might have a word processor 'engine' developed by ACME, Inc that is used as a basic word processor. Then, Extra, Inc might develop some writting tools that just plug right in increasign the functionality, and The TableMaker Co might add specialized table tools to it,...etc. Then, you could pick and choose what features you wanted, or not wanted. And The TableMaker Co's tools might also work with the spreadsheet engine, the drawing rpogram...
nice