I do a lot of "hot" labels linked to a cell. Click on the graph, click on the formula bar space, type "=" and then click on the cell. Finish by clicking the green check in the formula bar or Enter. The new text will appear in the middle of the graph. Move it to desired location.
If you're trying to label lots of data-related labels (ie, next to the data pts), I think you could probably use one of the chart labeler addins, specify the labels to appear offset (above, right, left, etc) and then select and move them as a group.
With individual labels that need their positions tweaked, I find the mouse to be a blunt instrument. Instead, I select the text box, hit F2 (edit) and then Esc. This leaves the focus on the text box and allows you to use the cursor arrows to fine tune the positioning. Cool thing is when the focus is on one text box, you can use the tab key to loop through selecting the other text boxes and sequentially tweak them, too, without having to select each one with the mouse (big time saver!).
g'luck
wbd