I find that the more guidelines I use on the page, they all start to mess up. For example, I have 2 90 degree guidlines and I want to put one on top of the other so I can move it else where to a certain measurement. If I have 5 or so guidelines already, when I drag guideline 1 to guideline 2, guideline 2 highlights a thick blue line and guideline 1 positions itself a noticeable distance away from guideline 2. Also, If I center more than 2 guidelines in varying angles (90,0,45) either they will center correctly or form some reason they form a very very very tiny right triangle. Or if there are just 2 guidelines and I try to place a node over the intersection, it acts as if there are 2 intersections (this is all with grid off because I don't use grids and grids arent' on when I start up)
Acer Aspire 7750G-6857/ 2.5 GHz with Turbo Boost up to 3.1 GHx/ Windows 7 64 bit/ Intel Core i5-2450M/ Radeon graphics HD 7670M 1GB VRAM/ AMD Dynamic Switchable Graphics/ 6GB DDR3 Memory/ 500GB HDO/ Acer Nplify 802.11 b/g/n