Another thing to remember is some longer focal length 1.25" eyepieces, particularly if they are a wide-field design, will definitely 'vignette' in a 1.25" barlow.
I cannot use my 20mm Meade QX with my current barlow (a 'generic' one, but I suspect it's the same as the Orion Shorty) because of severe vignetting. It looks a bit like this:
<img src="http://www.users.bigpond.net.au/trufflehunter/vignetting.jpg">
The first circle is what it looks like thru the ep w/o the barlow, the second circle with the barlow!
Definitely looking for a decent 2" barlow...