The R (for restricted) can be removed after you've done 100 hours instructing, upon the recommendation of a suitable CFI.
Shunter,
Quite right, but you must add the 25 solo signoffs, which cannot be 1st solo or 1st solo cross country. These are REALLY difficult to obtain. I work at a busy school and I've done 200+ hours instructional but only 11 solo signoffs. It's a bit galling to get someone to 1st solo standard and have to hand over to a more experienced instructor to send them solo, but treat it as an apprenticeship. In retrospect, it's quite good really, it allows you to learn the ropes under the wing of more experienced people. I reckon it's going to take me at least a year full-time to get the restriction removed.
TheOddOne