Initially I steered clear of add-ons, worried that I might download some virus infected zip file or an add-on that might completely corrupt my installation. However, having spent too long getting to too many instances, I started by downloading Carbonite to help me get from A to B. I have steadily added to the list over the year, and now have about 15 installed. Not all are "live" at a given time, and, being on a high-population, under-powered and laggy server (Eonar) I hate that I have to log out before I go "naked" into WinterGrasp and "minimal" into 25 mans (quartz timers & mirror, ORA2, DBM, FuBar, LibFuBarPlugin and, until it failed on me in Naxx, Decursive).

So adding something like X-perl that changes the GUI is a big step as I don't know what impact it will have on performance. The main benefits I can see already are that: it improves instantly my ability to see the MT and other's targets instantly; I can see which de-buffs and DoTs or HoTs I have on my target as these are shown larger than other people's.

Only had one problem with it so far, an irritation rather than fatal. The new quests in the Tournament give you a mount. When my mount died, I did not get my toolbars back, so was unable to cast flight form and had to walk back to the mount line. Not fatal for me, but might have been were it a PvP server!

Healbot. Having read the comments about it being complicated, I was reluctant to install this. The last thing you want as a healer it to be spending time working out wtf you need to do. However, so far no issues with it. I did try Decursive and grid, but when decursive failed to include a box for the MT (who happens to be my Guild Master too) in Naxx on Wednesday, I almost got saddled with the repair bill for two 10-man wipes on Maexxna ...

I'll let you know how I get on.