I love that it’s lightweight, I love that it’s innocuous, I love that it’s super-easy to use, and I love that it’s regularly updated. Couldn’t ask for a better tool for this purpose.
UPDATE: I’m still a huge supporter of Sip, I even blogged about how great it is a couple of years ago. Wouldn’t want to live without it. However, one surprising gaffe by the developer with this new release is the taking over of at least two basic, universal key commands: option left/right arrow. These are important commands for text editing - they jump the cursor one word to the left or right - and as such they should NEVER be messed with. Obviously these commands can be deleted in the preferences, and I can’t bring myself to ding you a star just for that because the app is still awesome, but I strongly advise the developer to remove these as defaults ASAP.
UPDATE 2: Fixed! I discovered the (very prompt, thank you!) update just as I discovered that Sip was also commandeering cmd-shift-C for the Color Palette, but that’s also a critical shortcut for Illustrator (centers text alignment). I killed that shortcut before performing the update, so I don’t know if that was also changed with version 4.0.2, but I’m probably not the only designer to complain about this issue, so I imagine it was. :)